Patent Publication Number: US-2011055294-A1

Title: Cellular terminal device, e-mail deletion method, and recording medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to and claims priority to Japanese Patent Application No. 2009-204073 filed on Sep. 3, 2009 and herein incorporated by reference. 
     FIELD 
     Various embodiments described herein relate to a cellular terminal device, an electronic mail (e-mail) deletion method, and a recording medium. 
     BACKGROUND 
     A cellular terminal device such as a cellular phone in a typical operation thereof may receive an e-mail, and store the received e-mail on a storage area called a received mail box. If no memory space is available in the mail box, no e-mail can be stored on the mail box. In such a case, an e-mail having the oldest reception time and date in the mail box is deleted to make a memory space, and a newly received e-mail is then stored on the received mail box. 
     If the mails are successively deleted in the order of reception from old to new, an e-mail that should not be deleted can be from time to time deleted. To avoid this situation, a user may perform a complicated operation for protecting important mails. If the user forgets protecting an important e-mail, that important e-mail is deemed to be automatically deleted. 
     In a related art technique, an e-mail sorted to a particular folder is deleted with a higher priority in order to overcome the problem that an important e-mail is automatically deleted. If an e-mail of the kind that the deletion thereof presents no problem is set to be sorted to the particular folder, unwanted e-mails can be automatically deleted with a higher priority. 
     In a proposed related art technique, a priority is attached to each e-mail in accordance with a condition set by the user, and a low-priority e-mail is deleted with a higher priority. The set condition here refers to a map of priority to a transmission source address of an e-mail, for example. In accordance with the related art technique, the priority of the transmission source address as a deletion target is set to be lower such that an automatic and unintended deletion of an important e-mail is prevented. For example, Japanese Laid-open Patent Publication No. 2006-235841, Japanese Laid-open Patent Publication No. 2002-278896, Japanese Laid-open Patent Publication No. 2006-134200, and Japanese Laid-open Patent Publication No. 2008-152578 are known as related art. 
     Each of the above-described related art techniques causes the user to be conscious of “which e-mail is to be deleted.” The user needs to pay attention to each e-mail. 
     With the typical technique of sorting the e-mails to a particular folder, the user needs to determine whether to sort each e-mail to the particular folder. With the typical technique of attaching the priority to the e-mail in accordance with the uniformly set condition, the user needs to determine how the priority of a sender address is to be set. 
     SUMMARY 
     It is an aspect of the embodiments discussed herein to provide a cellular terminal device including a memory for storing a received e-mail, a deletion order determiner for determining a deletion order of a plurality of e-mails stored on the memory based on an operation of a user or history information related to a mail sender and a deletion processor for deleting an e-mail stored on the memory in accordance with the deletion order determined by the deletion order determiner. 
     Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a structure of a cellular terminal device of an embodiment. 
         FIG. 2  illustrates a structure of a cellular terminal device of an embodiment. 
         FIG. 3  illustrates an operation trend information storage unit. 
         FIG. 4  illustrates a related information storage unit. 
         FIG. 5  illustrates a received mail storage unit. 
         FIG. 6  is a flowchart illustrating an operation trend information gathering process of the operation trend information gatherer illustrated in  FIG. 2 . 
         FIG. 7  is a flowchart illustrating a mail check process of a received mail checking unit illustrated in  FIG. 2 . 
         FIG. 8  is a flowchart illustrating a manual protection information gathering process of a manual protection information gathering unit illustrated in  FIG. 2 . 
         FIG. 9  is a flowchart illustrating a deletion order determination process of a deletion order determiner illustrated in  FIG. 2 . 
         FIG. 10  is a flowchart illustrating a deletion process of a deletion processor illustrated in  FIG. 2 . 
         FIG. 11  illustrates a structure of a cellular terminal device of an embodiment. 
         FIG. 12  illustrates an operation trend information storage unit. 
         FIG. 13  illustrates a related information storage unit. 
         FIG. 14  is a flowchart illustrating an operation trend information gathering process of an operation trend information gatherer illustrated in  FIG. 11 . 
         FIG. 15  is a flowchart illustrating a manual deletion information gathering process of a manual deletion information gathering unit illustrated in  FIG. 11 . 
         FIG. 16  is a flowchart illustrating a mail view information gathering process of a mail view information gathering unit illustrated in  FIG. 11 . 
         FIG. 17  is a flowchart illustrating an cellular terminal device internal information gathering process of a cellular terminal internal information gathering unit. 
         FIG. 18  illustrates an e-mail deletion process. 
         FIG. 19  illustrates a computer executing a cellular terminal control program. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     A cellular terminal device, an e-mail deletion method, and a recording medium to be disclosed in the application are described in detail below with reference to the drawings. The cellular terminal device, the e-mail deletion method, and the recording medium are not limited to the embodiments described herein. 
     A structure of a cellular terminal device  10  of an embodiment is described below with reference to  FIG. 1 .  FIG. 1  illustrates the structure of the cellular terminal device  10 . Referring to  FIG. 1 , the cellular terminal device  10  has a function of receiving an e-mail. Upon receiving an e-mail, the cellular terminal device  10  stores the received e-mail on a specific storage area. If the cellular terminal device  10  of an embodiment receives an e-mail with no memory space available for the e-mail, the cellular terminal device  10  automatically deletes from the specific storage area an e-mail that is likely to become unnecessary for the user. Elements of the cellular terminal device  10  are described below in detail. 
     Referring to  FIG. 1 , the cellular terminal device  10  of an embodiment includes a storage  11 , a deletion order determiner  12 , a deletion processor  13 , and a storage controller  14 . The storage  11  stores a received e-mail. A size of an e-mail the storage  11  can store is typically specified. For example, a number of e-mails to be stored on the storage  11  is specified or a total size of e-mails to be stored on the storage  11  is specified. 
     The deletion order determiner  12  determines a deletion order of a plurality of e-mails stored on the storage  11  in accordance history information of operation(s) of a user or history information about a relation between the user and a sender of the e-mail stored on the storage  11 . More specifically, the deletion order determiner  12  determines the deletion order of e-mails likely to become unnecessary for the user in accordance with the history information. The determination of the deletion order may be based on a plurality of factors relating to history information including that pertains to the user and/or use of the cellular terminal device  10 . 
     If a new e-mail is received with no memory space available on the storage  11 , the deletion processor  13  performs a deletion process to delete an e-mail stored on the storage  11  in the deletion order determined by the deletion order determiner  12 . After the deletion processor  13  performs the deletion process, the storage controller  14  stores a newly received e-mail on the storage  11 . 
     The cellular terminal device  10  of an embodiment determines the deletion order of a plurality of e-mails stored on the storage  11  in response to an operation of the user or the history information about the relation between the user and the mail sender. When a new e-mail is received, the cellular terminal device  10  performs the deletion process on the e-mail stored on the storage  11  in accordance with the deletion order, and stores the new e-mail on the storage  11 . The cellular terminal device  10  of an embodiment automatically deletes the e-mails in an order according to which the e-mails are likely to become unnecessary for the user. 
     The cellular terminal device  10  of an embodiment dynamically determines the deletion order of the e-mails in accordance with the operation history of the user. The e-mails likely to become unnecessary for the user are efficiently deleted without the need for the user to be conscious of the e-mail as an automatic deletion target. 
     The cellular terminal device of an embodiment is specifically discussed. In accordance with an embodiment, information related to an e-mail deleted by the user and information related to an e-mail protected by the user are used as history information. 
     ((Structure of the Cellular Terminal Device of an Embodiment)) Referring to  FIG. 2 , a structure of a cellular terminal device  100  of an embodiment is described below.  FIG. 2  illustrates the structure of the cellular terminal device  100  of an embodiment. The cellular terminal device  100  of an embodiment is a cellular telephone or a personal digital assistant (PDA), for example. Referring to  FIG. 2 , the cellular terminal device  100  includes an antenna  110 , a communication controller  120 , an input unit  130 , a display  140 , a storage  150 , and a controller  160 . 
     The antenna  110  transmits a signal to and receives a signal from the outside. For example, the antenna  110  transmits an e-mail to and receives an e-mail from an external information process apparatus. The communication controller  120  performs communication control on voice communication and data communication via a base station (not illustrated). 
     The input unit  130  is an input device for inputting a variety of information and an operation instruction. For example, the input unit  130  includes alphanumerical keys for inputting numbers and characters, and cursor keys for selecting a menu, and for scrolling operations. The display  140  is an output device for outputting a variety of information, and includes a liquid-crystal device, and a loudspeaker. 
     The storage  150  is a storage device for storing a variety of information. The storage  150  includes a random-access memory (RAM), or a flash memory. Referring to  FIG. 2 , the storage  150  of an embodiment includes an operation trend information storage unit  151 , a related information storage unit  152 , and a received mail storage unit  153 . 
     The operation trend information storage unit  151  stores information indicating an operation trend of the user using each e-mail stored on the received mail storage unit  153  (hereinafter referred to as “operation trend information”).  FIG. 3  illustrates an example of an operation trend information storage unit  151 . The “storage period” stores on a per specific storage period basis the total number of e-mails deleted by the user. Referring to  FIG. 3 , the storage period is categorized into “shorter than 10 minutes,” “10 minutes or longer and shorter than 1 day,” and “1 day or longer.” 
     The operation trend information storage unit  151  of  FIG. 3  indicates that the number of e-mails that have a storage period “shorter than 10 minutes” from the mail reception of the cellular terminal device  100  to the mail deletion by the user is “10 mails.” The operation trend information storage unit  151  of  FIG. 3  indicates that the number of e-mails that have a storage period “10 minutes or longer and shorter than 1 day” from the mail reception of the cellular terminal device  100  to the mail deletion by the user is “5 mails.” The operation trend information storage unit  151  of  FIG. 3  indicates that the number of e-mails that have a storage period “longer than 1 day” from the mail reception of the cellular terminal device  100  to the mail deletion by the user is “20 mails.” 
     In the operation trend information storage unit  151  of  FIG. 3 , the user of the cellular terminal device  100  tends to delete an e-mail after the elapse of 1 day or longer after mail reception. Moreover in the operation trend information storage unit  151  of  FIG. 3 , the user of the cellular terminal device  100  is less likely to delete an e-mail that elapsed 10 minutes or longer but not elapsed 1 day from the mail reception. The cellular terminal device  100  can thus identify the trend of the e-mails to be deleted by the user in accordance with a variety of information stored on the operation trend information storage unit  151 . While a specific operation trend is illustrated in association with  FIG. 3 , the present invention is not limited to any particular trend. For example, trend information may be tracked based on any processing of an email received from sender(s) such that a number of particular processing(s) results in the email being indicated for deletion. 
     The related information storage unit  152  stores a variety of information indicating the importance of each e-mail for each of the senders having sent the e-mails stored on the received mail storage unit  153 . In other words, the related information storage unit  152  stores information related to a mail sender of an e-mail being important for the user. In the discussion that follows, the variety of information to be stored on the related information storage unit  152  is sometimes referred to as “related information.”  FIG. 4  illustrates an example of the related information storage unit  152 . Referring to  FIG. 4 , the related information storage unit  152  of an embodiment stores items such as “sender, “total reception count,” “protected mail count,” and “deletion point.” 
     The “sender” indicates sender information of the e-mail received by the cellular terminal device  100 . For example, a transmission source address, and a sender name of a sender are stored at the “sender.” The “total reception count” indicates a number of e-mails transmitted by the “sender” from among the e-mails stored on the cellular terminal device  100 . The “protected mail count” indicates the number of e-mails protected by the user from among the corresponding “total reception count.” 
     The “deletion point” is an indicator that is used to determine the deletion order. The “deletion point” is updated by a deletion order determiner  163 . The “deletion point” is described in detail later together with the deletion order determiner  163 . 
     A first row of the related information storage unit  152  illustrated in  FIG. 4  indicates that the number of e-mails received from a sender “A” is “50,” and that the number of e-mails protected by the user out of the 50 e-mails is “0.” A second row of the related information storage unit  152  illustrated in  FIG. 4  indicates that the number of e-mails received from a sender “B” is “30,” and that the number of e-mails protected by the user out of the 30 e-mails is “3.” A third row of the related information storage unit  152  illustrated in  FIG. 4  indicates that the number of e-mails received from a sender “C” is “10,” and that the number of e-mails protected by the user out of the 10 e-mails is “2.” 
     In the related information storage unit  152  of  FIG. 4 , the cellular terminal device  100  receives e-mails more from the sender “A” than e-mails from each of the senders “B” and “C.” The user of the cellular terminal device  100  is less likely to protect the e-mails received from the sender “A,” and more likely to protect the e-mails received from the sender “C.” The trend of the e-mail protected by the user is learned based on a variety of information stored on the related information storage unit  152 . 
     The cellular terminal device  100  identifies the senders of the e-mails more important for the user based on the variety of information stored on the related information storage unit  152 . The user is more likely to protect the e-mail received from the sender “C,” and the e-mail received from the sender “C” is considered to be an important e-mail for the user of the cellular terminal device  100 . 
     The received mail storage unit  153  stores the received e-mail. The received mail storage unit  153  may also be referred to as a received mail box.  FIG. 5  illustrates an example of the received mail storage unit  153 . Referring to  FIG. 5 , the received mail storage unit  153  of an embodiment stores items such as “mail identification information,” “sender,” “reception time and date,” “protection status,” and “deletion order.” The received mail storage unit  153  may also store header information of an e-mail, and data of a body of the e-mail, although not illustrated in  FIG. 5 . 
     The “mail identification information” identifies an e-mail. The “sender” stores sender information of an e-mail identified by the “mail identification information.” The “reception time and date” indicates time and date of reception of the e-mail identified by the “mail identification information.” The “protection status” indicates whether the e-mail identified by the “mail identification information” is protected by the user or not. If the “protection status” is “0” in  FIG. 5 , the e-mail is not protected, and if the “protection status” is “1,” the e-mail is protected. 
     The “deletion order” indicates a deletion order of a plurality of e-mails stored on the received mail storage unit  153 . In accordance with an embodiment, an e-mail having a smaller value for the “deletion order” is deleted with a higher priority. The “deletion order” is updated by the deletion order determiner  163  to be discussed later. The “deletion order” is also described later in the discussion of the deletion order determiner  163 . 
     A first row of the received mail storage unit  153  in  FIG. 5  indicates that the sender of the e-mail identified by the mail identification information “M 11 ” is “A” and that the time and date of reception of the e-mail is 10:15, Aug. 5, 2009, and that the e-mail is not protected. A second row of the received mail storage unit  153  in  FIG. 5  indicates that the sender of the e-mail identified by the mail identification information “M 12 ” is “B” and that the time and date of reception of the e-mail is 10:12, Aug. 5, 2009, and that the e-mail is not protected. 
     The controller  160  includes an internal memory storing a program defining a variety of calculation processes, and executes the variety of calculation processes. Referring to  FIG. 2 , the controller  160  includes an operation trend information gatherer  161 , a related information gatherer  162 , a deletion order determiner  163 , a deletion processor  164 , and a storage control unit  165 . 
     The operation trend information gatherer  161  gathers operation trend information, and stores the gathered operation trend information onto the operation trend information storage unit  151 . More specifically, if an e-mail is deleted from the received mail storage unit  153  by the user, the operation trend information gatherer  161  of an embodiment calculates a period throughout which the e-mail was stored on the received mail storage unit  153 . The operation trend information gatherer  161  then increments the storage period on the operation trend information storage unit  151  in response to the calculated period. 
     For example, the user may now delete an e-mail that has elapsed 5 minutes since the storage thereof on the received mail storage unit  153 . In other words, the user deletes the e-mail 5 minutes after the reception of the e-mail by the cellular terminal device  100 . The operation trend information gatherer  161  increments a value stored at the storage period “shorter than 10 minutes” on the operation trend information storage unit  151 . For example, if “10” is stored at the storage period “shorter than 10 minutes” on the operation trend information storage unit  151  as illustrated in  FIG. 3 , “10” stored at the storage period “shorter than 10 minutes” is updated to “11.” 
     The user may delete an e-mail that has elapsed 3 hours since the storage thereof on the received mail storage unit  153 . The operation trend information gatherer  161  increments a value stored at the storage period “10 minutes or longer and shorter than 1 day” on the operation trend information storage unit  151 . The user may delete an e-mail that has elapsed 2 days since the storage thereof on the received mail storage unit  153 . The operation trend information gatherer  161  increments a value stored at the storage period “1 day or longer” on the operation trend information storage unit  151 . 
     The related information gatherer  162  gathers related information, and stores the gather related information on the related information storage unit  152 . The related information gatherer  162  of an embodiment includes a received mail checking unit  162   a  and a manual protection information gathering unit  162   b.    
     The received mail checking unit  162   a  updates the total reception count on the related information storage unit  152 . More specifically, the received mail checking unit  162   a  increments the total reception count on the related information storage unit  152  corresponding to the sender of an e-mail if the e-mail is received. 
     The related information storage unit  152  may now be in the state illustrated in  FIG. 4 . If an e-mail is received from the sender “A,” the received mail checking unit  162   a  updates the total reception count on the related information storage unit  152  corresponding to the sender “A” from “50” to “51.” If an e-mail is received from the sender “B,” the received mail checking unit  162   a  updates the total reception count on the related information storage unit  152  corresponding to the sender “B” from “30” to “31.” 
     The manual protection information gathering unit  162   b  updates the protected mail count on the related information storage unit  152 . More specifically, if an e-mail is protected by the user, the manual protection information gathering unit  162   b  increments the protected mail count on the related information storage unit  152  corresponding to the sender of the protected e-mail. 
     The related information storage unit  152  may now be in the state illustrated in  FIG. 4 . If the user protects an e-mail from the sender “A,” the manual protection information gathering unit  162   b  updates the protected mail count on the related information storage unit  152  corresponding to the sender “A” from “0” to “1.” If the user protects an e-mail from the sender “B,” the manual protection information gathering unit  162   b  updates the protected mail count on the related information storage unit  152  corresponding to the sender “B” from “3” to “4.” 
     The deletion order determiner  163  determines a deletion order of a plurality of e-mails stored on the received mail storage unit  153 , in accordance with a variety of information stored on the operation trend information storage unit  151  and a variety of information stored on the related information storage unit  152 . More specifically, the deletion order determiner  163  updates the deletion point on the related information storage unit  152 . The deletion order determiner  163  attaches the deletion point to each e-mail in the received mail storage unit  153 , in accordance with the operation trend information stored on the operation trend information storage unit  151  and the deletion point on the related information storage unit  152 . In accordance with the attached deletion point, the deletion order determiner  163  determines the deletion order of each e-mail stored on the received mail storage unit  153 . 
     The deletion order determination process of the deletion order determiner  163  is described below with reference to  FIGS. 3-5 . In the discussion that follows, the operation trend information storage unit  151  is in the state illustrated in  FIG. 3 , the related information storage unit  152  is in the state illustrated in  FIG. 4 , and the received mail storage unit  153  is in the state illustrated in  FIG. 5 . 
     The deletion order determiner  163  calculates a ratio of the protected mail count to the total reception count (hereinafter referred to a “protection ratio”) on a per sender basis in accordance with the variety of information stored the related information storage unit  152 . 
     More specifically, as illustrated in  FIG. 4 , the protected mail count for the sender “A” is “0,” and the deletion order determiner  163  calculates the protection ratio of the sender “A,” thereby obtaining “0%.” Referring to  FIG. 4 , the total reception count for the sender “B” is “30,” and the protected mail count is “3.” The deletion order determiner  163  divides the protected mail count “3” by the total reception count “30” to calculate the protection ratio of the sender “B,” thereby obtaining “0.1.” Referring to  FIG. 4 , the total reception count for the sender “C” is “10,” and the protected mail count is “2.” The deletion order determiner  163  divides the protected mail count “2” by the total reception count “10” to calculate the protection ratio of the sender “C,” thereby obtaining “0.2.” The deletion order determiner  163  thus calculates the protection ratio for each sender as follows:
         (a). Sender “A”: Protection ratio “0%”   (b). Sender “B”: Protection ratio “10%”   (c). Sender “C”: Protection ratio “20%”       

     From among the e-mails received from the senders A, B and C (A-C), the user of the cellular terminal device  100  is most likely to protect an e-mail received from the sender C, and more likely to protect an e-mail received from the sender B. In other words, the e-mail received from the sender C is the most important for the user of the cellular terminal device  100 . 
     The higher the protection ratio, the lower deletion point the deletion order determiner  163  sets, and the lower the protection ratio, the higher deletion point the deletion order determiner  163  sets. The deletion points for the protection ratios are determined as listed below:
         (a). Protection ratio 0%: Deletion point “+5”   (b). Protection ratio 1%-10%: Deletion point “+3”   (c). Protection ratio 11%-50%: Deletion point “+2”   (d). Protection ratio 51%-100%: Deletion point “+1”       

     Since the protection ratio for the sender “A” is “0%,” the deletion order determiner  163  updates the deletion point for the sender “A” to “5,” as illustrated in  FIG. 4 . Since the protection ratio for the sender “B” is “10%,” the deletion order determiner  163  updates the deletion point for the sender “B” to “3.” Since the protection ratio for the sender “C” is “20%,” the deletion order determiner  163  updates the deletion point for the sender “C” to “2.” 
     The deletion order determiner  163  calculates a ratio of the number of e-mails deleted during a specific storage period to the total number of e-mails deleted by the user (hereinafter referred to as a “storage period based deletion ratio”). 
     More specifically, the deletion order determiner  163  sums “10,” “5,” and “20” stored at the storage periods on the operation trend information storage unit  151 , thereby resulting in “35” as the total number of e-mails deleted by the user. The deletion order determiner  163  then divides the total number of e-mails “10” deleted during the storage period “shorter than 10 minutes” by the total number “35,” thereby resulting in “0.29” as the storage period based deletion ratio of the storage period “shorter than 10 minutes.” The deletion order determiner  163  then divides the total number of e-mails “5” deleted during the storage period “10 minutes or longer and shorter than 1 day” by the total number “35,” thereby resulting in “0.14” as the storage period based deletion ratio of the storage period “10 minutes or longer and shorter than 1 day.” The deletion order determiner  163  then divides the total number of e-mails “20” deleted during the storage period “longer than 1 day” by the total number “35,” thereby resulting in “0.57” as the storage period based deletion ratio of the storage period “longer than 1 day.” In the above example, the deletion order determiner  163  rounds the division results to the nearest hundredth. In summary, the deletion order determiner  163  calculates the protection ratio for each sender as listed below:
         (a). Storage period “shorter than 10 minutes”:
           Storage period based deletion ratio “29%”   
           (b). Storage period “10 minutes or longer and shorter than 1 day”:
           Storage period based deletion ratio “14%”   
           (c). Storage period “longer than 1 day”:
           Storage period based deletion ratio “57%”   
               

     From the above listing, the user of the cellular terminal device  100  is less likely to protect an e-mail having a storage period “10 minutes or longer and shorter than 1 day”, and more likely to protect an e-mail having a storage period “longer than 1 day.” 
     To attach the deletion point to an e-mail stored on the received mail storage unit  153 , the deletion order determiner  163  calculates a period from the storage of the e-mail on the received mail storage unit  153  to the present time. The higher the storage period based deletion ratio responsive to the calculated period, the higher deletion point the deletion order determiner  163  thus attaches to the e-mail. The lower the storage period based deletion ratio responsive to the calculated period, the lower deletion point the deletion order determiner  163  thus attaches to the e-mail. The deletion point is determined to the storage period based deletion ratio as listed below:
         (a). Storage period based deletion ratio 0%-20%:
           Deletion point “+0”   
           (b). Storage period based deletion ratio 21%-50%:
           Deletion point “+1”   
           (c). Storage period based deletion ratio 51%-100%:
           Deletion point “+3”   
               

     In such a case, the deletion order determiner  163  adds a deletion point of “1” to an e-mail having a storage period “shorter than 10 minutes” from the storage thereof on the received mail storage unit  153  to the present time. The deletion order determiner  163  adds no deletion point to an e-mail having a storage period “10 minutes or longer and shorter than 1 day” from the storage thereof on the received mail storage unit  153  to the present time. The deletion order determiner  163  adds a deletion point of “3” to an e-mail having a storage period “longer than 1 day” from the storage thereof on the received mail storage unit  153  to the present time. 
     The received mail storage unit  153  illustrated in  FIG. 5  is described below. The present time here is “200908051020.” The deletion order determiner  163  retrieves from the received mail storage unit  153  illustrated in  FIG. 5  information about the sender “A” corresponding to the mail identification information “M 11 ” and the reception time and date “200908051015.” The deletion order determiner  163  retrieves a deletion point of “5” corresponding to the sender “A” from the related information storage unit  152 . The deletion order determiner  163  attaches a deletion point of “5” to the e-mail identified by the mail identification information “M 11 .” 
     The deletion order determiner  163  calculates a storage period of the e-mail stored on the received mail storage unit  153  and identified the mail identification information “M 11 .” Since the present time is “200908051020” and the reception time and date of the e-mail identified by the mail identification information “M 11 ” is “200908051015,” the deletion order determiner  163  results in a storage time of “5 minutes” by calculating a difference between the present time and the reception time and date. Since the storage time of “5 minutes” is “shorter than 10 minutes,” the deletion order determiner  163  adds a deletion point of “1” to the e-mail identified by the mail identification information “M 11 .” More specifically, the deletion order determiner  163  attaches a deletion point of “5+1”=“6” to the e-mail identified by the mail identification information “M 11 .” 
     The deletion order determiner  163  performs the above-described process to each e-mail stored on the received mail storage unit  153 . As a result, the deletion order determiner  163  attaches the following deletion points to the e-mails identified by the mail identification information “M 11 ”-“M 15 .”
         (a). Mail identification information “M 11 ”:
           Deletion point “5+1”=“6”   
           (b). Mail identification information “M 12 ”:
           Deletion point “3+1”=“4”   
           (c). Mail identification information “M 13 ”:
           Deletion point “5+0”=“5”   
           (d). Mail identification information “M 14 ”:
           Deletion point “2+3”=“5”   
           (e). Mail identification information “M 15 ”:
           Deletion point “5+3”=“8”   
               

     As a larger deletion point is attached to an e-mail, the deletion order determiner  163  sets a smaller deletion order to that e-mail. For example, the received mail storage unit  153  may now store only five e-mails identified by the mail identification information “M 11 ”-“M 15 ,” as illustrated in  FIG. 5 . The deletion order determiner  163  sets a deletion order “ 1 ” to the e-mail identified by the mail identification information “M 15 ” having the highest deletion point. The deletion order determiner  163  sets a deletion order “ 2 ” to the e-mail identified by the mail identification information “M 11 ” having the second highest deletion point. The deletion order determiner  163  sets a deletion order “ 3 ” to the e-mail identified by the mail identification information “M 13 ” having the third highest deletion point. The deletion order determiner  163  sets a deletion order “ 4 ” to the e-mail identified by the mail identification information “M 12 ” having the fourth highest deletion point. The deletion order determiner  163  sets no deletion order to the e-mail identified by the mail identification information “M 14 ” having a protection status of “1.” 
     The deletion order determiner  163  determines in this way the deletion order of each e-mail stored on the received mail storage unit  153 . As previously described, the deletion order determiner  163  determines the deletion order based on the operation trend information indicating the operation trend of the user and the related information indicating the importance of each mail. More specifically, the deletion order determiner  163  can determine the deletion order of the e-mails in the order of high to low likeliness of the e-mail becoming unnecessary for the user. 
     In order to receive a new e-mail, the deletion processor  164  deletes the e-mails stored on the received mail storage unit  153  in the deletion order determined by the deletion order determiner  163 . More specifically, if no memory space is available on the received mail storage unit  153 , the deletion processor  164  deletes e-mails from the received mail storage unit  153  in the deletion order determined by the deletion order determiner  163 . Two examples of the deletion process of the deletion processor  164  are described below. 
     When a new e-mail is received, the deletion processor  164  retrieves, from header information or the like, information about a size of the e-mail to be received. If a memory space available on the received mail storage unit  153  is smaller than the size of the e-mail to be received, the received mail storage unit  153  deletes an e-mail having the smallest value in the deletion order stored on the received mail storage unit  153 . The deletion processor  164  deletes e-mails having the smallest values in the deletion order stored on the received mail storage unit  153  until the memory space available on the received mail storage unit  153  becomes larger than the size of the e-mail to be received. 
     Alternatively, in order to receive a new e-mail, the deletion processor  164  determines whether the number of received e-mails stored on the received mail storage unit  153  has reached a specific number. The “specific number” is a given number and represents a maximum number of e-mails the cellular terminal device  100  can store. If the number of received e-mails stored on the received mail storage unit  153  reaches the specific number, the deletion processor  164  deletes an e-mail having the smaller number in the deletion order stored on the received mail storage unit  153 . 
     The storage control unit  165  stores a newly received e-mail on the received mail storage unit  153  after the deletion processor  164  deletes the e-mail. 
     ((Process of the Cellular Terminal Device  100  of an Embodiment)) A process of the cellular terminal device  100  of an embodiment is described with reference to  FIGS. 6-10 . 
     An operation trend information gathering process of the operation trend information gatherer  161  illustrated in  FIG. 2  is described below with reference to  FIG. 6 .  FIG. 6  is a flowchart illustrating the operation trend information gathering process of the operation trend information gatherer  161  of  FIG. 2 . Referring to  FIG. 6 , if an e-mail is deleted from the received mail storage unit  153  by the user (yes branch from operation S 101 ), the operation trend information gatherer  161  calculates the storage period of the deleted e-mail (operation S 102 ). For example, the operation trend information gatherer  161  calculates the storage period of the e-mail by determining a difference between the present time and the reception time and date of the deleted e-mail. 
     The operation trend information gatherer  161  increments the storage period on the operation trend information storage unit  151  in response to the storage period calculated in operation S 102  (operation S 103 ). For example, if the storage period of the e-mail deleted by the user is “5 minutes,” the operation trend information gatherer  161  increments the value stored on the storage period “shorter than 10 minutes” on the operation trend information storage unit  151  illustrated in  FIG. 3 . 
     Referring to  FIG. 7 , a mail checking process of the received mail checking unit  162   a  illustrated in  FIG. 2  is described in detail below.  FIG. 7  is a flowchart of the mail checking process performed by the received mail checking unit  162   a  illustrated in  FIG. 2 . An e-mail is received as illustrated in  FIG. 7  (yes branch from operation S 201 ), the received mail checking unit  162   a  retrieves sender information of the received e-mail (operation S 202 ). For example, the received mail checking unit  162   a  retrieves a mail address of a transmission source as the sender information from header information or the like of the received e-mail. 
     The received mail checking unit  162   a  increments the total reception count on the related information storage unit  152  in response to the sender information retrieved in operation S 202  (operation S 203 ). For example, if an e-mail is received from the sender “A,” the received mail checking unit  162   a  increments a value at the total reception count on the related information storage unit  152  for the sender “A.” 
     Referring to  FIG. 8 , a manual protection information gathering process of the manual protection information gathering unit  162   b  illustrated in  FIG. 2  is described below.  FIG. 8  is a flowchart illustrating the manual protection information gathering process of the manual protection information gathering unit  162   b  of  FIG. 2 . Referring to  FIG. 8 , if an e-mail is protected by the user (yes branch from operation S 301 ), the manual protection information gathering unit  162   b  retrieves the sender information of the protected e-mail (operation S 302 ). For example, the manual protection information gathering unit  162   b  retrieves the sender information of the protected e-mail from information stored at the sender on the received mail storage unit  153 . 
     The manual protection information gathering unit  162   b  increments the protected mail count on the related information storage unit  152  in response to the sender information retrieved in operation S 302  (operation S 303 ). For example, the e-mail corresponding to the mail identification information “M 14 ” out of the e-mails stored on the received mail storage unit  153  illustrated in  FIG. 5  is an e-mail protected by the user. In such a case, the manual protection information gathering unit  162   b  retrieves information of the sender “C” corresponding to the mail identification information “M 14 .” The manual protection information gathering unit  162   b  increments the value stored at the protected mail count on the related information storage unit  152  in response to the retrieved information of the sender “C.” 
     Referring to  FIG. 9 , a deletion order determination process of the deletion order determiner  163  of  FIG. 2  is described below.  FIG. 9  is a flowchart illustrating the deletion order determination process of the deletion order determiner  163  illustrated in  FIG. 2 . Referring to  FIG. 9 , the deletion order determiner  163  retrieves from the related information storage unit  152  information stored at the “total reception count,” and the “protected mail count” on a per sender basis (operation S 401 ). For example, the deletion order determiner  163  retrieves form the related information storage unit  152  a total reception count “50” and a protected mail count “0” for the sender “A.” 
     The deletion order determiner  163  then calculates the protection ratio based on the “total reception count” and the “protected mail count” retrieved in operation S 401  (operation S 402 ). For example, the deletion order determiner  163  may retrieve the protection ratio based on a total reception count “50” and a protected mail count “0” for the sender “A” in operation S 401 . The deletion order determiner  163  thus results in “0%” as the protection ratio for the sender “A.” For example, the deletion order determiner  163  may retrieve the protection ratio based on a total reception count “30” and a protected mail count “3” for the sender “B” in operation S 401 . The deletion order determiner  163  thus results in “10%” as the protection ratio for the sender “B.” 
     If the protection ratio calculation of all the senders with information related to the senders stored on the related information storage unit  152  is not completed (no branch from operation S 403 ), the deletion order determiner  163  performs the protection ratio calculation in operations S 401  and S 402  for a remaining sender. 
     If the protection ratio calculation of all the senders with the information related to the senders stored on the related information storage unit  152  is completed (yes branch from operation S 403 ), the deletion order determiner  163  updates the deletion point on the related information storage unit  152  for the protection ratio (operation S 404 ). More specifically, the deletion order determiner  163  sets a smaller value for the deletion point as the protection ratio is higher, and sets a larger value for the deletion point as the protection ratio is lower. 
     The deletion order determiner  163  calculates the storage period based deletion ratio based on the variety of information stored on the operation trend information storage unit  151  (operation S 405 ). The deletion order determiner  163  retrieves from the received mail storage unit  153  the information stored at the “sender” and the “reception time and date” for each e-mail (operation S 406 ). The deletion order determiner  163  retrieves the deletion point corresponding to the “sender” retrieved in operation S 405  (operation S 407 ). 
     The deletion order determiner  163  calculates the storage period of the e-mail as a process target on the received mail storage unit  153 , based on the present time and the “reception time and date” retrieved in operation S 406  (operation S 408 ). The deletion order determiner  163  determines the deletion point, based on the calculated storage period and the storage period based deletion ratio calculated in operation S 405  (operation S 409 ). The deletion order determiner  163  then sums the deletion point retrieved in operation S 407  and the deletion point determined in operation S 409 , and attaches the point sum to the e-mail as the process target (operation S 410 ). 
     If the deletion point attachment process is not completed for all the e-mails stored on the received mail storage unit  153  (no branch from operation S 411 ), the deletion order determiner  163  performs the process operations in operations S 406 -S 410  for an unprocessed e-mail. 
     If the deletion point attachment process is completed for all the e-mails stored on the received mail storage unit  153  (yes branch from operation S 411 ), the deletion order determiner  163  determines the deletion order of the e-mails (operation S 412 ). More specifically, the deletion order determiner  163  determines the deletion order of each e-mail based on the deletion points provided in operation S 411 . 
     The deletion order determiner  163  periodically performs the deletion order determination process. For example, the deletion order determiner  163  performs the deletion order determination process every few hours or every day. Alternatively, the deletion order determiner  163  may perform the deletion order determination process when the cellular terminal device  100  is not used by the user. Alternatively, the deletion order determiner  163  may perform the deletion order determination process in a time band throughout which the user is less likely to use the cellular terminal device  100 . 
     Referring to  FIG. 10 , a deletion process of the deletion processor  164  of  FIG. 2  is described.  FIG. 10  is a flowchart of the deletion process of the deletion processor  164  illustrated in  FIG. 2 . Referring to  FIG. 10 , if a new e-mail is received (yes branch from operation S 501 ), the deletion processor  164  retrieves information of a size of the received e-mail (operation S 502 ). 
     If a memory space is available on the received mail storage unit  153  (yes branch from operation S 503 ), the deletion processor  164  ends the process. If no memory space is available on the received mail storage unit  153  (no branch from operation S 503 ), the deletion processor  164  deletes e-mails from the received mail storage unit  153  in accordance with the information stored at the deletion order on the received mail storage unit  153  (operation S 504 ). More specifically, the deletion processor  164  deletes an e-mail having the smallest value at the deletion order on the received mail storage unit  153 . 
     If no memory space is available on the received mail storage unit  153  even with the e-mail deleted (no branch from operation S 505 ), the deletion processor  164  performs operation S 504  again. If a memory space is available on the received mail storage unit  153  (yes branch from operation S 505 ), the deletion processor  164  ends the process. 
     Subsequent to the deletion process of the deletion processor  164 , the storage control unit  165  stores on the received mail storage unit  153  the e-mail received in operation S 501  (operation S 506 ). 
     As described above, the cellular terminal device  100  of an embodiment gathers the operation trend information indicating the operation trend of the user, and determines the deletion order of the e-mail in accordance with the gathered operation trend information. The cellular terminal device  100  of an embodiment deletes, with a higher priority, the e-mail likely to be deleted by the user. 
     The cellular terminal device  100  of an embodiment gathers the related information indicating the importance of each e-mail stored on the received mail storage unit  153 , and determines the deletion order in accordance with the gathered related information. The cellular terminal device  100  of an embodiment can delete, with a higher priority, an e-mail less important for the user. 
     Each time an e-mail deletion operation is performed by the user, the cellular terminal device  100  of an embodiment gathers an operation trend information and the related information. Each time an e-mail deletion operation is performed, the cellular terminal device  100  of an embodiment can update the deletion order of the e-mails. More specifically, the cellular terminal device  100  of an embodiment can dynamically detect an e-mail likely to become unnecessary for the user. According to an embodiment a setting of a deletion order is automatically implemented without requiring input of a user specifying the deletion order. 
     The cellular terminal device  100  of an embodiment gathers the operation trend information and the related information based on an operation history of the user. With the cellular terminal device  100  of an embodiment, the user can save them time for inputting information used to determine the deletion priority of the e-mail. 
     The cellular terminal device  100  of an embodiment can delete efficiently an e-mail likely to become unnecessary for the user without the user being conscious of an e-mail as an automatic deletion target. 
     In accordance with an embodiment, a storage period is used as the operation trend information and the protected mail count or the protection ratio is used as the related information as illustrated in  FIGS. 3 and 4 . The cellular terminal device disclosed in the application may use other information as the operation trend information and the related information. In accordance with an embodiment, other information is used as the operation trend information and the related information. 
     ((Structure of Cellular Terminal Device of an Embodiment)) A cellular terminal device  200  of an embodiment is described below with reference to  FIG. 11 .  FIG. 11  illustrates a structure of the cellular terminal device  200  of an embodiment. Referring to  FIG. 11 , the cellular terminal device  200  includes an antenna  110 , a communication controller  120 , an input unit  130 , a display  140 , a storage  250 , and a controller  260 . Elements identical in function to those illustrated in  FIG. 2  are designated with the same reference numerals and the detailed discussion thereof is omitted here. 
     The storage  250  includes an operation trend information storage unit  251 , a related information storage unit  252 , and a received mail storage unit  153 .  FIG. 12  illustrates the example of the operation trend information storage unit  251 . Referring to  FIG. 12 , the operation trend information storage unit  251  of an embodiment stores items such as a “keyword,” and a “mail body length.” 
     The “keyword” represents a number of e-mails deleted by the user, each including a specific character string included in subjects (titles) or mail bodies thereof. The operation trend information storage unit  251  illustrated in  FIG. 12  indicates that the number of e-mails, each e-mail including the phrase “all right” in the subject or the mail body thereof, out of the e-mails deleted by the user, is “5.” The operation trend information storage unit  251  illustrated in  FIG. 12  indicates that the number of e-mails, each e-mail including the word “thanks” in the subject or the mail body thereof, out of the e-mails deleted by the user, is “2.” The operation trend information storage unit  251  illustrated in  FIG. 12  indicates that the number of e-mails, each e-mail including the word “sorry” in the subject or the mail body thereof, out of the e-mails deleted by the user, is “0.” 
     The “mail body length” represents the total number of e-mails deleted by the user on a per length or size basis of the mail body of the deleted e-mail. The operation trend information storage unit  251  illustrated in  FIG. 2  indicates that the number of e-mails having a mail body length of “10 characters or less” out of the e-mails deleted by the user is “10.” The operation trend information storage unit  251  illustrated in  FIG. 2  indicates that the number of e-mails having a mail body length of “11 to 50 characters” out of the e-mails deleted by the user is “5.” The operation trend information storage unit  251  illustrated in  FIG. 2  indicates that the number of e-mails having a mail body length of “51 characters or more” out of the e-mails deleted by the user is “1.” 
     With the operation trend information storage unit  251  in the state illustrated in  FIG. 12 , the user of the cellular terminal device  200  is likely to delete an e-mail including “all right” in the subject or the mail body thereof. With the operation trend information storage unit  251  in the state illustrated in  FIG. 12 , the user of the cellular terminal device  200  is likely to delete an e-mail having a mail body length “10 characters or less.” The deletion order determiner  263  identifies the trend of the e-mail to be deleted by the user, based on the variety of information stored on the operation trend information storage unit  251 . 
       FIG. 13  illustrates an example of the related information storage unit  252 . Referring to  FIG. 13 , the related information storage unit  252  of an embodiment includes new items such as a “manual deletion count,” a “view completion count,” a “reply count,” a “telephone book registration status,” an “incoming telephone call count,” an “outgoing telephone call count,” and a “mail transmission count.” 
     The “manual deletion count” indicates the number of e-mails deleted by the user, out of the “total reception count.” The “view completion count” indicates the number of e-mails that have been viewed to the last line of the mail body by the user out of the “total reception count.” The “reply count” indicates the number of e-mails that the user has replied to, out of the “total reception count.” 
     The “telephone book registration status” indicates whether information related to the “sender” is registered in telephone book information. The “telephone book information” here includes a telephone number, a mail address, etc. If the “telephone book registration status” is “0” in  FIG. 13 , information corresponding to the “sender” is not registered in the telephone book information. If the “telephone book registration status” is “1” in  FIG. 13 , information corresponding to the “sender” is registered in the telephone book information. 
     The “incoming telephone call count” indicates the number of incoming telephone calls made by the “sender.” The “outgoing telephone call count” indicates the number of outgoing telephone calls the user has made to the “sender.” The “mail transmission count” indicates the total number of e-mails transmitted to the “sender.” 
     A first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that the number of e-mails received from the sender “A” is “50.” The first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that the number of e-mails deleted by the user, out of the 50 e-mails, is “10,” and that the number of e-mails that the user has viewed to the last lines of the mail bodies is “40.” The first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that the number of e-mails that the user has replied to, out of the 50 e-mails received from the sender “A”, is “10.” The first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that a telephone number and a mail address of the sender “A” are registered in the telephone book information. The first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that the number of incoming telephone calls from the sender “A” is “10” and that the number of outgoing telephone calls to the sender “A” is “15.” The first row of the related information storage unit  252  illustrated in  FIG. 13  indicates that the total number of e-mails to the sender “A” is “40.” 
     With the related information storage unit  252  in the state of  FIG. 13 , the cellular terminal device  200  receives many more e-mails from the sender “A” than e-mails from each of the senders “B” and “C.” However, the user of the cellular terminal device  200  is less likely to delete the e-mails received from the sender “C” than the e-mails received from each of the senders “A” and “B.” The user of the cellular terminal device  200  is more likely to view the e-mail from the sender “C” to the last line of the e-mail than the e-mails from the senders “A” and “B.” 
     Based on a variety of information stored on the related information storage unit  252 , the cellular terminal device  200  may identify the trend of the e-mails important for the user on a per sender basis. In the above example, the user of the cellular terminal device  200  is less likely to delete the e-mails from the sender “C” and more likely to view the e-mails from the sender “C” to the last lines of the e-mails. It is thus considered that the e-mails received from the sender “C” are important for the user of the cellular terminal device  200 . 
     The user of the cellular terminal device  200  does not register information related to the user “C” on the telephone book information. The user receives incoming telephone calls from the sender “C” at a lower frequency than those from each of the senders “A” and “B” and transmits outgoing telephone calls to the sender “C” at a lower frequency than those to the other senders. The user also transmits e-mails to the sender “C” at a lower frequency than those to each of the senders “A” and “B.” 
     Given these pieces of information, the cellular terminal device  200  may identify a frequency of contacts between the user and the sender of the e-mails based on the variety of information stored on the related information storage unit  252 . An e-mail transmitted from a sender having a low frequency of contacts may be considered less important for the user. In the above example, the e-mail received from the sender “C” may be considered less important for the user of the cellular terminal device  200 . 
     The deletion order determiner  263  to be discussed later sets the deletion point on a per sender basis based on the information stored at each item illustrated in  FIG. 13 . The process of the deletion order determiner  263  is described in detail below. 
     If an e-mail is deleted from the received mail storage unit  153  by the user, the operation trend information gatherer  261  determines whether a specific keyword is included in the deleted e-mail. If the specific keyword is included in the deleted e-mail, the operation trend information gatherer  261  increments the value stored on the operation trend information storage unit  251  corresponding to the keyword. Also, if the e-mail is deleted from the received mail storage unit  153  by the user, the operation trend information gatherer  261  retrieves a mail body length of the deleted e-mail. The operation trend information gatherer  261  increments the value on the operation trend information storage unit  251  in response to the retrieved mail body length. 
     The user may delete an e-mail including the phrase “all right” in the mail body and having a mail body length of “8 characters.” In such a case, the operation trend information gatherer  261  increments the value stored at the keyword “all right” on the operation trend information storage unit  251  and the value stored at the mail body length “10 characters or less” on the operation trend information storage unit  251 . 
     The related information gatherer  262  includes a received mail checking unit  162   a , a manual protection information gathering unit  162   b , a manual deletion information gathering unit  262   c , a mail view information gathering unit  262   d , and a cellular terminal internal information gathering unit  262   e.    
     The manual deletion information gathering unit  262   c  updates the manual deletion count on the related information storage unit  252 . More specifically, if an e-mail is deleted by the user, the manual deletion information gathering unit  262   c  retrieves the sender information of the deleted e-mail, and increments the manual deletion count on the related information storage unit  252  in response to the retrieved sender information. 
     The related information storage unit  252  may be now in the state as illustrated in  FIG. 13 . If an e-mail from the sender “A” is deleted by the user, the manual deletion information gathering unit  262   c  updates “10” at the manual deletion count on the related information storage unit  252  corresponding to the sender “A” to “11.” 
     The mail view information gathering unit  262   d  updates the view completion count and the reply count on the related information storage unit  252 . More specifically, if a received e-mail is viewed to the last line of the mail body by the user, the related information gatherer  262  retrieves the sender information of the e-mail, and increments the view completion count on the related information storage unit  252  in response to the retrieved sender information. For example, if the word “END” indicating the last line of the mail body is displayed on the display  140 , the mail view information gathering unit  262   d  determines that the received e-mail has been viewed to the last line thereof. 
     If a reply operation is performed on a received e-mail by the user, the mail view information gathering unit  262   d  retrieves the sender information of the e-mail, and increments the reply count on the related information storage unit  252  in response to the retrieved sender information. 
     The cellular terminal internal information gathering unit  262   e  updates the incoming telephone call count, the outgoing telephone call count, and the mail transmission count on the related information storage unit  252 . More specifically, the cellular terminal internal information gathering unit  262   e  sums the incoming telephone call count, the outgoing telephone call count, and the mail transmission count on a per sender basis based on the telephone book information, outgoing telephone call history, incoming telephone call history, etc. The cellular terminal internal information gathering unit  262   e  updates the incoming telephone call count, the outgoing telephone call count, and the mail transmission count on the related information storage unit  252  in response the sum results. 
     The deletion order determiner  263  determines a deletion order of a plurality of e-mails stored on the received mail storage unit  153 , based on the variety of information stored on the operation trend information storage unit  251  and the variety of information stored on the related information storage unit  252 . 
     More specifically, the deletion order determiner  263  updates the deletion point on the related information storage unit  252 . As the deletion order determiner  163  in an embodiment, the deletion order determiner  263  calculates the protection ratio on a per sender basis. The deletion order determiner  263  also calculates a ratio of the manual deletion count to the total reception count (hereinafter referred to as a “deletion ratio”). The deletion order determiner  263  also calculates a ratio of the view completion count to the total reception count (hereinafter referred to as a “view ratio”). The deletion order determiner  263  also calculates a ratio of the reply count to the total reception count (hereinafter referred to as a “reply ratio”). 
     As the deletion order determiner  163  in an embodiment, the deletion order determiner  263  sets a smaller value to the deletion point as the protection ratio is higher, and sets a larger value to the deletion point as the protection ratio is lower. 
     The deletion order determiner  263  sets a larger value to the deletion point as the deletion ratio is higher, and sets a smaller value to the deletion point as the deletion ratio is lower. This is because an e-mail transmitted from a sender having a low deletion ratio is considered to be important for the user. 
     The deletion order determiner  263  sets a smaller value to the deletion point as the view ratio is higher, and sets a larger value to the deletion point as the view ratio is lower. This is because an e-mail transmitted from a sender having a high view ratio is considered to be important for the user. 
     The deletion order determiner  263  sets a smaller value to the deletion point as the reply ratio is higher, and sets a larger value to the deletion point as the reply ratio is lower. This is because an e-mail transmitted from a sender having a high reply ratio is considered to be important for the user. 
     The deletion order determiner  263  adds the deletion point to a sender having “0 (not registered)” stored on the telephone book registration status. The deletion order determiner  263  adds no deletion point to a sender having “1 (registered)” stored on the telephone book registration status. This is because an e-mail transmitted from a sender registered on the telephone book information is considered to be important for the user. 
     If a large value is stored at the incoming telephone call count, the deletion order determiner  263  sets a small value to the corresponding deletion point, and if a small value is stored at the incoming telephone call count, the deletion order determiner  263  sets a large value to the corresponding deletion point. The frequency of contacts with a sender having a high incoming telephone call count is considered to be high, and an e-mail from the sender is thus considered to be important for the user. For the same reason, if a large value is stored at the outgoing telephone call count or the mail transmission count, the deletion order determiner  263  sets a small value to the deletion point, and if a small value is stored at the outgoing telephone call count or the mail transmission count, the deletion order determiner  263  sets a large value to the deletion point. 
     On the basis of the information stored on the operation trend information storage unit  251 , the deletion order determiner  263  calculates a ratio of the number of mails including a specific keyword to the total number of e-mails deleted by the user (hereinafter referred to as a “keyword based deletion ratio”). The deletion order determiner  263  calculates a ratio of the number of e-mails having a mail body length falling within a specific range to the total number of e-mails deleted by the user (hereinafter referred to as a “mail body length based deletion ratio”). 
     When a deletion point is attached to an e-mail stored on the received mail storage unit  153 , the deletion order determiner  263  determines whether a specific keyword is included in the mail body of the e-mail. If a specific keyword is included in the mail body of the e-mail, the deletion order determiner  263  attaches a larger value deletion point to the e-mail as the keyword based deletion ratio responsive to the keyword is higher. Also, when a deletion point is attached to an e-mail stored on the received mail storage unit  153 , the deletion order determiner  263  retrieves a mail body length of the e-mail. The deletion order determiner  263  attaches a larger value deletion point to the e-mail as the mail body length based deletion ratio responsive to the retrieved mail body length is higher. 
     ((Process of the Cellular Terminal Device  200  of an Embodiment)) A process of each element of the cellular terminal device  200  of an embodiment is described below with reference to  FIGS. 14-17 . 
     Referring to  FIG. 14 , an operation trend information gathering process of the operation trend information gatherer  261  illustrated in  FIG. 11  is described below.  FIG. 14  is a flowchart of the operation trend information gathering process of the operation trend information gatherer  261  illustrated in  FIG. 11 . If an e-mail is deleted from the received mail storage unit  153  by the user (yes branch from operation S 601 ), the operation trend information gatherer  261  determines whether a specific keyword is included in the deleted e-mail (operation S 602 ). 
     If the specific keyword is included in the deleted e-mail (yes branch from operation S 602 ), the operation trend information gatherer  261  increments the value on the operation trend information storage unit  251  corresponding to the keyword (operation S 603 ). 
     The operation trend information gatherer  261  retrieves the mail body length of the deleted e-mail (operation S 604 ). The operation trend information gatherer  261  increments the value on the operation trend information storage unit  251  in response to the retrieved mail body length (operation S 605 ). 
     Referring to  FIG. 15 , a manual deletion information gathering process of the manual deletion information gathering unit  262   c  illustrated in  FIG. 11  is described below.  FIG. 15  is a flowchart of the manual deletion information gathering process of the manual deletion information gathering unit  262   c  illustrated in  FIG. 11 . If an e-mail is deleted by the user as illustrated in  FIG. 15  (yes branch from operation S 710 ), the manual deletion information gathering unit  262   c  retrieves the sender information of the deleted e-mail (operation S 702 ). The manual deletion information gathering unit  262   c  increments the manual deletion count on the related information storage unit  252  in response to the retrieved sender information (operation S 703 ). 
     Referring to  FIG. 16 , a mail view information gathering process of the mail view information gathering unit  262   d  illustrated in  FIG. 11  is described below.  FIG. 16  is a flowchart of the mail view information gathering process of the mail view information gathering unit  262   d  illustrated in  FIG. 11 . If a received e-mail is viewed to the last line thereof by the user (yes branch from operation S 801 ) as illustrated in  FIG. 16 , the mail view information gathering unit  262   d  retrieves the sender information of the e-mail (operation S 802 ). The mail view information gathering unit  262   d  increments the view completion count on the related information storage unit  252  in response to the retrieved sender information (operation S 803 ). 
     If a reply operation is performed to the received e-mail by the user (yes branch from operation S 804 ), the mail view information gathering unit  262   d  retrieves the sender information as a reply destination of the e-mail (operation S 805 ). The mail view information gathering unit  262   d  increments the reply count on the related information storage unit  252  in response to the retrieved sender information (operation S 806 ). 
     Referring to  FIG. 17 , a cellular terminal internal information gathering process of the cellular terminal internal information gathering unit  262   e  illustrated in  FIG. 11  is described below.  FIG. 17  is a flowchart of the cellular terminal internal information gathering process of the cellular terminal internal information gathering unit  262   e  illustrated in  FIG. 11 . As illustrated in  FIG. 17 , the cellular terminal internal information gathering unit  262   e  retrieves information stored at the sender on the related information storage unit  252  (operation S 901 ). 
     The cellular terminal internal information gathering unit  262   e  determines whether the sender information retrieved in operation S 901  is registered in the telephone book information (operation S 902 ). If the sender information is registered in the telephone book information (yes branch from operation S 902 ), the cellular terminal internal information gathering unit  262   e  updates the telephone book registration status on the related information storage unit  252  corresponding to the sender information to “1 (registered)” (operation S 903 ). If the sender information is not registered in telephone book information (no branch from operation S 902 ), the cellular terminal internal information gathering unit  262   e  updates the telephone book registration status on the related information storage unit  252  corresponding to the sender information to “0 (not registered)” (operation S 904 ). 
     The cellular terminal internal information gathering unit  262   e  sums incoming telephone calls from the sender indicated by the sender information retrieved in operation S 901 , based on the telephone book information, the incoming call history, and the outgoing call history. The cellular terminal internal information gathering unit  262   e  updates the incoming telephone call count on the related information storage unit  252  corresponding to the sender information with the call sum. 
     On the basis of the telephone book information or the like, the cellular terminal internal information gathering unit  262   e  sums outgoing telephone calls to the sender indicated by the sender information retrieved in operation S 901 . The cellular terminal internal information gathering unit  262   e  updates the outgoing telephone call count on the related information storage unit  252  corresponding to the sender information with the call sum (operation S 906 ). 
     The cellular terminal internal information gathering unit  262   e  sums the total number of e-mails transmitted to the sender indicated by the sender information retrieved in operation S 901 . The cellular terminal internal information gathering unit  262   e  updates the mail transmission count on the related information storage unit  252  corresponding to the sender information with the transmission sum (operation S 907 ). 
     If the process for all the senders listed on the related information storage unit  252  is not completed (no branch from operation S 908 ), the cellular terminal internal information gathering unit  262   e  performs operations S 901 -S 907  for a remaining sender. If the process for all the senders listed on the related information storage unit  252  is completed (yes branch from operation S 908 ), the cellular terminal internal information gathering unit  262   e  ends the process. 
     As described above, the cellular terminal device  200  of an embodiment gathers the operation trend information and the related information indicating the frequency of contacts between the user and the sender, based on the operation history of the user, the telephone book information, and the like, and then determines the deletion order of the e-mails. The cellular terminal device  200  of an embodiment can thus delete, with a higher priority, the e-mail likely to be deleted by the user. The cellular terminal device  200  of the third embodiment can determine the deletion order of the e-mails based on the frequency of contacts with the user. 
     The cellular terminal device disclosed in the application may be embodied in an arrangement different from the above-described embodiments. An embodiment of the cellular terminal device is described below. 
     ((Deletion Process)) In accordance with at least some of the above-described embodiments, the cellular terminal device deletes the e-mails in accordance with the deletion order. The cellular terminal device disclosed in the application may delete the e-mails, depending on the size of a newly received e-mail, regardless of the deletion order. Such cellular terminal device is described with reference to  FIG. 18 .  FIG. 18  illustrates an example of the e-mail deletion process. The received mail storage unit  153  illustrated in  FIG. 18  stores five e-mails respectively identified by mail identification information “M 21 ”-“M 25 .” The received mail storage unit  153  has now no memory space available. 
     As illustrated in an upper portion of  FIG. 18 , the e-mail identified by the mail identification information “M 25 ” has a deletion order “ 1 ,” the e-mail identified by the mail identification information “M 21 ” has a deletion order “ 2 ,” and the e-mail identified by the mail identification information “M 23 ” has a deletion order of “ 3 .” The e-mails identified by the mail identification information “M 25 ” and the mail identification information “M 21 ” have a size of “2 Kbytes,” and the e-mail identified by the mail identification information “M 23 ” has a size of “2 Mbytes.” 
     In this condition, an e-mail having a size of “1 Mbytes” is now being received. In accordance with the above-described embodiments, the e-mail identified by the mail identification information “M 25 ” is deleted first. The available memory space on the received mail storage unit  153  is thus increased by “2 Kbytes.” The e-mail identified by the mail identification information “M 21 ” is further deleted in accordance with the above-described embodiments, if a newly received 1 Mbyte e-mail cannot be stored on the received mail storage unit  153 . The e-mail identified by the mail identification information “M 23 ” is deleted in accordance with the above-described embodiments if the memory space on the received mail storage unit  153  is still insufficient after the e-mail identified by the mail identification information “M 21 ” is deleted. If the three e-mails identified by the mail identification information “M 25 ,” “M 21 ,” and “M 23 ” are deleted, the space available on the received mail storage unit  153  increases to “2.4 Mbytes,” and the newly received e-mail can be stored on the received mail storage unit  153 . 
     The cellular terminal device of the at least some of above-described embodiments may delete only the e-mail identified by the mail identification information “M 23 ” rather than deleting three e-mails identified by the mail identification information “M 25 ,” “M 21 ,” and “M 23 .” Through this deletion, the space available on the received mail storage unit  153  increases by “2 Mbytes.” The cellular terminal device of each of the above-described embodiments can store the newly received 1 Mbyte e-mail on the received mail storage unit  153 . The cellular terminal device of each of the above-described embodiments may delete only an e-mail larger in size than a newly received e-mail if the e-mail larger in size than the newly received e-mail is included in the e-mails as deletion targets. The cellular terminal device disclosed in the application can thus delay the timing of deletion of the e-mails. 
     In accordance with at least some of the above-described embodiments, the deletion order of the e-mails is determined in accordance with the varieties of information illustrated in  FIGS. 3 ,  4 ,  12 , and  13 . For example, the cellular terminal device  100  of an embodiment determines the deletion order of the e-mails based on the storage period illustrated in  FIG. 3 , and the protected mail count illustrated in  FIG. 4 . The cellular terminal device disclosed in the application may determine the deletion order of the e-mails based on other information. 
     For example, if an e-mail is deleted by the user, the cellular terminal device disclosed in the application may determine whether the deleted e-mail is a Deco mail (registered trademark). The cellular terminal device may then store information indicating whether the Deco mail tends to be deleted. Such an operation, if performed by the cellular terminal device  200  of an embodiment, for example, is described below. The operation trend information gatherer  261  in the cellular terminal device  200  causes the operation trend information storage unit  251  to store the total number of Deco mails. On the basis of the information gathered by the operation trend information gatherer  261 , the deletion order determiner  263  in the cellular terminal device  200  adds a deletion point to the Deco mail if the Deco mail is likely to be deleted by the user. 
     The cellular terminal device disclosed in the application may determine the deletion order of the e-mails on the basis of the total number of unread e-mails, and the number of accesses to a uniform resource locator (URL) included in the mail body. Such an operation, if performed by the cellular terminal device  200  of an embodiment, for example, is described below. The mail view information gathering unit  262   d  in the cellular terminal device  200  determines whether a received e-mail has been viewed by the user, and causes the related information storage unit  252  to store the number of e-mails unviewed (hereinafter referred to as an “unviewed mail count”). The mail view information gathering unit  262   d  determines whether the URL included in the mail body of the received e-mail has been accessed, and then causes the related information storage unit  252  to store the number of accessed e-mails. The deletion order determiner  263  in the cellular terminal device  200  sets a larger value to the deletion point as a ratio of the unviewed mail count to the total reception count is higher. For example, the deletion order determiner  263  in the cellular terminal device  200  sets a larger value to the deletion point as a ratio of the number of URL accesses to the total reception count is lower. 
     The cellular terminal device disclosed in the application may evacuate, to a specific storage area, specific information such as a mail address included in the mail body of a mail to be deleted, a telephone number, and a URL if the e-mail is automatically deleted. The cellular terminal device disclosed in the application may allow the user to view the evacuated specific information. 
     The above-described processes may be performed when a computer, such as a personal computer or a workstation, executes a prepared program. Referring to  FIG. 19 , a computer  1000  having the same function as that of the cellular terminal device  10  illustrated in  FIG. 1  and executing a cellular terminal control program is described below. 
     According to an embodiment, a condition of a deletion order is automatically adjusted based on trend information pertaining to processing of an email and at least some of emails stored in a memory are deleted based on the deletion order as adjusted. A condition for an order of deleting stored emails is set automatically based on information of processing of emails and without requiring a user to manually specify the order. 
       FIG. 19  illustrates the computer  1000  executing the cellular terminal control program. Referring to  FIG. 19 , the computer  1000  includes a random-access memory (RAM)  1010 , a cache  1020 , a hard disk drive (HDD)  1030 , a read-only memory (ROM)  1040 , a central processing unit (CPU)  1050 , and a bus  1060 . The RAM  1010 , the cache  1020 , the HDD  1030 , the ROM  1040 , and the CPU  1050  are interconnected to each other via the bus  1060 . 
     The ROM  1040  pre-stores the cellular terminal control program for performing the same function as that of the cellular terminal device  10  illustrated in  FIG. 1 . More specifically, the ROM  1040  store a deletion order determination program  1041 , a deletion process program  1042 , and a storage control program  1043 . 
     The CPU  1050  reads and executes the deletion order determination program  1041 , the deletion process program  1042 , and the storage control program  1043 . Referring to  FIG. 19 , the deletion order determination program  1041  controls a deletion order determination process  1051 , the deletion process program  1042  controls a deletion process  1052 , and the storage control program  1043  controls a storage control process  1053 . The deletion order determination process  1051  corresponds to the deletion order determiner  12  illustrated in  FIG. 1 , the deletion process  1052  corresponds to the deletion processor  13  illustrated in  FIG. 1 , and the storage control process  1053  corresponds to the storage controller  14  illustrated in  FIG. 1 . 
     The HDD  1030  includes a mail storage unit  1031 . The mail storage unit  1031  corresponds to the storage  11  illustrated in  FIG. 1 . 
     It is not a requirement that each of the programs  1041 - 1043  be stored on the ROM  1040 . For example, each of the programs  1041 - 1043  may be stored on a “removable physical medium” loaded onto the computer  1000 , such as a flexible disk (FD), a compact-disk ROM (CD-ROM), a magneto-optical (MO) disk, a digital versatile disk (DVD), or an IC card. Each of the programs  1041 - 1043  may be stored on a “fixed physical medium,” internal to or external to the cellular terminal device  100 , such as a hard disk drive (HDD). Each of the programs  1041 - 1043  may be stored on another “computer (or server)” connected to the cellular terminal device  100  via a public telephone line, the Internet, a local-area network (LAN), or a wide-area network (WAN). The computer  1000  may read the program from the medium, such as the flexible disk, for execution. 
     As described above, the embodiments can be implemented in computing hardware (computing apparatus) and/or software, such as (in a non-limiting example) any computer that can store, retrieve, process and/or output data and/or communicate with other computers. The results produced can be displayed on a display of the computing hardware. A program/software implementing the embodiments may be recorded on computer-readable media comprising computer-readable recording media. The program/software implementing the embodiments may also be transmitted over transmission communication media. Examples of the computer-readable recording media include a magnetic recording apparatus, an optical disk, a magneto-optical disk, and/or a semiconductor memory (for example, RAM, ROM, etc.). Examples of the magnetic recording apparatus include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape (MT). Examples of the optical disk include a DVD (Digital Versatile Disc), a DVD-RAM, a CD-ROM (Compact Disc-Read Only Memory), and a CD-R (Recordable)/RW. An example of communication media includes a carrier-wave signal. 
     Further, according to an aspect of the embodiments, any combinations of the described features, functions and/or operations can be provided. 
     Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.