Abstract:
The invention relates to a method for communicating information between a first wireless communication device ( 10 ) and a communications network ( 30 ) via a particular second wireless communication device ( 20 ), the communications network being said second wireless communication device&#39;s own communications network. In the method, the user identification data of said first wireless communication device ( 10 ) is transmitted to said second wireless communication device ( 20 ). In the method, said second wireless communication device ( 20 ) makes a contact to its own communications network ( 30 ) on the basis of the user identification data of said first wireless communication device ( 10 ) for communicating information between the first wireless communication device ( 10 ) and said communications network ( 30 ) via said second wireless communication device ( 20 ). The invention also relates to said first and second communications devices ( 10, 20 ).

Description:
FIELD OF THE INVENTION 
   The present invention relates to an arrangement for communicating information between a first wireless communication device and a communications network via a particular second wireless communication device. Especially, but not necessarily, the invention relates to providing a communications network service to the first wireless communication device via the second wireless communication device. 
   BACKGROUND OF THE INVENTION 
   Electronic devices, such as so called palmtop computers, i.e. PDA (Personal Digital Assistant) devices, do not usually have expensive radio modem functions, such as GSM (Global System for Mobile Communications) functions, integrated into one and the same device. This type of devices are often also mobile and, thus, do not have a fixed wire connection to the network. There is, however, an increasing need to access the Internet and/or a local network from such electronic devices. 
   Bluetooth technology provides an inexpensive way of integrating a radio modem into many electronic devices. However, the range of the Bluetooth link, usually from approximately ten meters to a few hundred meters, does not generally allow an electronic device having a Bluetooth transceiver to reach an access point. An access point refers herein to a device coupled to a desired network, such as the Internet or a local network, such as an Ethernet local area network. 
   European patent application number EP 00660132.2 discloses an interesting arrangement for communicating user identification data to a wireless communication device. According to the application, a user data identification device to which a user data identification module, such as a SIM (Subscriber Identity Module) card, is inserted is arranged separate from the wireless communication device. The user data identification module contains the user identification data of the user of the wireless communication device. 
   The user data identification device and the wireless communication device are connected to each other by means of a local link (e.g. Bluetooth link). Upon switching on the wireless communication device it requests the user identification data from the user data identification device over the local link. The user identification data is sent to the wireless communication device as a response to said request. 
   Since the user data identification device with its identification module is now implemented as a separate device from the wireless communication device, the wireless communication device can be made smaller. The invention disclosed in the patent application makes it possible for more than one wireless communication device (e.g. a portable computer and a mobile station of the GSM system) to simultaneously fetch the user identification data from the identification module in the user data identification device, in which case the user can even use these different wireless communication devices simultaneously. 
   European patent application EP 00660132.2 does not, however, provide a solution to the problematic situation, in which the wireless communication device cannot with its short-range connection reach the access point for accessing a desired network. 
   The wireless communication device may have means for establishing a Bluetooth link, but it may be outside the Bluetooth range from the access point and it may lack other means for establishing a direct connection to the desired network. The other means refer, for instance, to means for establishing a longer-range radio connection to the desired network, in which case a short range refers to a range of approximately ten meters to three hundred meters achieved by a Bluetooth link, for instance, and a longer range refers to a range longer than this. A GSM cellular network connection, for instance, can have a range of over 30 kilometers. Alternatively, the other means only refer to means for establishing a connection to an available network regardless of the range. 
   SUMMARY OF THE INVENTION 
   Now, a new invention has been made. According to a first aspect of the invention there is provided a method for communicating information between a first wireless communication device and a communications network via a particular second wireless communication device, the communications network being said second wireless communication device&#39;s own communications network, in which method 
   user identification data of said first wireless communication device is supplied to said second wireless communication device. 
   It is characteristic of the method that it comprises: 
   making a contact from said second wireless communication device to its own communications network on the basis of the user identification data of said first wireless communication device for communicating information between the first wireless communication device and said communications network via said second wireless communication device. 
   According to a second aspect of the invention there is provided a wireless communication device which is arranged to communicate information with a communications network via a particular second wireless communication device, the communications network being said second wireless communication device&#39;s own communications network, the wireless communication device comprising 
   means for supplying user identification data of the wireless communication device to said second wireless communication device. 
   It is characteristic of the the wireless communication device that it comprises: 
   means for causing said second wireless communication device to make a contact to said second wireless communication device&#39;s own communications network on the basis of the user identification data of said wireless communication device for communicating information between the wireless communication device and said communications network via said second wireless communication device. 
   According to a third aspect of the invention there is provided a wireless communication device which is arranged to transfer information via itself between a particular second wireless communication device and a communications network the communications network being the wireless communication device&#39;s own communications network, the wireless communication device comprising 
   means for receiving user identification data of said second wireless communication device. 
   It is characteristic of the wireless communication device that it comprises: 
   means for making a contact from the wireless communication device to its own communications network on the basis of the user identification data of said second wireless communication device for communicating information between the second wireless communication device and said communications network via the wireless communication device. 
   The second wireless communication device&#39;s own communications network refers herein to the closest network in which said second wireless communication device is designed to operate. If said second wireless communication device is a wireless communication device of a cellular network, for instance, its own communications network is the cellular network. Especially if said second wireless communication device is that of the GSM or UMTS (Universal Mobile Telecommunications System, a third-generation mobile network) network, the network of said second wireless communication device is the GSM or UMTS network, respectively. 
   Said contact making refers, for instance, to the second wireless communication device making a contact for registering to its own network using the user identification data of the user of said first wireless communication device, or to making a contact for establishing a data transfer connection, for instance a cellular network connection, between said second wireless communication device and said communications network on the basis of the user identification data transferred from said first wireless communication device. 
   According to a preferred embodiment of the invention, the first wireless communication device is arranged to have a short-range link to the second wireless communication device. Said second wireless communication device comprises means for making a contact to its own network. The user identification data of the first wireless communication device is transmitted over the short-range link to said second wireless communication device. Said identification data preferably comprises an IMSI (International Mobile Subscriber Identity) code, or the like, of the user of said first wireless communication device. 
   In an embodiment of the invention, said second wireless communication device establishes on the initiative of the first wireless communication device a connection, on behalf of the first wireless communication device, to its own communications network and transfers information, such as data, speech, multimedia or streaming-type information, for instance, between the first wireless communication device and said communications network. The second wireless communication device&#39;s own network preferably has a link to a third network, which may be the Internet or a local, preferably IP-based (Internet Protocol) network. In this way, the second wireless communication device can provide the first wireless communication device access to a network desired by the first wireless communication device, in such a manner, however, that billing the connection is done on the basis of the user identification data of the first wireless communication device. This is due to the fact that said second wireless communication device uses the user identification data of the first wireless communication device when establishing the connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be described in detail with reference to the accompanying drawings, in which  FIG. 1  illustrates a basic arrangement in a preferred embodiment of the invention,  FIG. 2  illustrates in greater detail an arrangement of a preferred embodiment of the invention,  FIG. 3  illustrates a data transfer method in a preferred embodiment of the invention,  FIG. 4  illustrates exchanging messages in a preferred embodiment of the invention, and  FIG. 5  illustrates a particular second embodiment of the invention. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates a basic arrangement in a preferred embodiment of the invention. It comprises a first wireless communication device  10 , a second wireless communication device  20 , and a communications network  30 , to which the first wireless communication device desires to establish a connection. The first wireless communication device  10  comprises a short-range transceiver, but may lack means for establishing a direct connection to the communications network  30 . The second wireless communication device  20  comprises means for making a connection to the communications network  30 . According to the invention, the first wireless communication device  10  establishes a connection to the second wireless communication device  20  over a local link  12 , and the second wireless communication device establishes a connection  32  to the desired communications network  30 . In this way, an indirect connection is provided from the first wireless communication device  10  through the second wireless communication device  20  to the available communications network  30 . The connection  32  from the second wireless communication device  20  to the desired communications network  30  is, however, authenticated with the user identification data of the first wireless communication device  10 , thus allowing a network operator to bill the user of the first wireless communication device  10  for the connection  32 . The invention thus makes it possible for the user of the first wireless communication device  10  to use the wireless communication device  20  of another user on his or her own account, without any costs arising to said another user. 
   In the following, the invention will be described using a PDA (Personal Digital Assistant) device as an example of the first wireless communication device  10  and a mobile station MS of a cellular network, such as a mobile station of the GSM network or a third-generation mobile network (e.g. UMTS), as an example of the second wireless communication device  20 . It is, however, clear that the invention can also be applied to other wireless communication devices. The first wireless communication device  10  can, for instance, be an electronic book, i.e. an eBook device, which contains a Bluetooth transceiver for loading information contents, such as pages of a book or newspaper, electronically into the eBook device for reading. The GSM cellular network is used as an example of the communications network  30 , to which the first wireless communication device  10  wants to establish a connection. Alternatively, the communications network  30  can be a UMTS cellular network. The GSM and UMTS networks have, in a manner known per se, a connection to the Internet via a suitable gateway, for instance, in which case if the first terminal is provided a connection to the UMTS network, for instance, it can via the connection access a local network or the Internet, from which the information content that the first terminal desires can be fetched. The Internet refers to the world-wide network of computer networks. The Internet may comprise local networks, the access to which may be limited. The gateway can be a WAP (Wireless Application Protocol) gateway, for instance. 
     FIG. 2  shows an arrangement according to a preferred embodiment of the invention, which comprises a PDA device  10 , a mobile station  20 , and a communications network  30 . Data transfer between the PDA device  10  and the mobile station  20  is arranged by means of a local link  12 . The local link is preferably established as an LPRF (Low Power Radio Frequency connection, e.g. Bluetooth technology, WLAN (Wireless Local Area Network) technology), but other methods, such as infra-red data transmission or an RS232 connection, can also be applied. The Bluetooth technology and WLAN technology use a frequency range or 2.4 GHz. The PDA device  10  comprises short-range data transmission means  13 , which comprise a transmitter TX and receiver RX, for providing a short-range data transfer connection  12  to the mobile station  20 . Corresponding short-range data transmission means  23  are arranged in the mobile station  20 , and they, too, comprise a transmitter TX and a receiver RX. The transmitter and receiver can be implemented separately, or integrated into one transceiver unit. 
   The PDA device  10  has a control unit  14  for controlling the operation of the PDA device  10 . The control unit preferably comprises a memory MEM and a processor MCU or the like, such as a micro-controller or microprocessor. The control unit  14  is coupled to the data transmission means  13  with a first control and data bus  17 . The PDA device  10  also comprises coupling means  15  for coupling the user data identification module  16  to the PDA device  10 . Said coupling means  15  are arranged to have a data transfer connection to the control unit  14  with a second control and data bus  18 . Via the second control and data bus  18 , the control unit  14  can, when necessary, read data from the user data identification module  16  and write data into it. The user data identification module is a SIM card or the like. (According to one proposal, a UIM (User Identification Module) card corresponds to the SIM card in a third-generation network (UMTS)). The coupling means  15  typically contain a slot for the SIM card and a smart card reader for reading data from and writing data to the SIM card. In addition, the PDA device  10  comprises a user interface Ul for using the PDA device. The user interface Ul may have a display for displaying information to the user and a keyboard for receiving input from the user into the PDA device. The user interface Ul is coupled to the control unit  14 . 
   The user data identification module  16  can also contain a control unit, coupling means, and memory, but these are not shown in the accompanying figures and are known to a person skilled in the art. In addition, the user data identification module  16  typically comprises means (not shown) for preventing unauthorised modification of the information (user identification information) in the user data identification module  16 . The user data identification module  16  can also be implemented by software in connection with the memory means MEM of the control unit  14 , for instance, in such a manner that stored data therein remains even when operating voltage is not switched on for the PDA device  10 . 
   The mobile station  20  comprises a control unit  24  for controlling the operation of the mobile station  20 . The control unit preferably comprises a memory MEM and a processor MCU or the like, such as a micro-controller or microprocessor. The control unit  24  is arranged to have a data transfer connection to the short-range data transmission means  23  of the mobile station over a third control and data bus  27 . The wireless communication device  20  comprises a radio part  33  for implementing cellular network functions. The radio part transmits and receives radio signals on a radio frequency which preferably differs from the radio frequency used by the local link  12 . The structure and operation of the radio part  33  is known to a person skilled in the art and, accordingly, need not be described in more detail herein. The radio part  33  is coupled to the control unit  24  with a fourth control and data bus  29 . The mobile station  20  also comprises coupling means  25 , known per se, for coupling the user data identification module  26  (SIM card or the like) to the mobile station  20 . Said coupling means  25  are arranged to have a data transfer connection to the control unit  24  with a fifth control and data bus  28 . Via the control and data bus  28 , the control unit  24  can, when necessary, read data from the user data identification module  26  and write data into it. In addition, the mobile station comprises a user interface Ul for using the mobile station. The user interface Ul may have a display for displaying information to the user and a keyboard for receiving input from the user into the mobile station. The user interface Ul is coupled to the control unit  24 . 
   In the following, the operation of the method of a preferred embodiment of the invention is described in the apparatus of  FIG. 2 . Let us assume that the user of the mobile station  20  has switched the operating voltage on to the mobile station, in which case the control unit  24  of the mobile station has taken the necessary initialisation steps to start up the operation of the mobile station  20 . Let us also assume that the user of the mobile station has inserted into the mobile station the user data identification module  26  (SIM card) which contains the user identification data of the mobile station. The user identification data is used to identify the user. The mobile station  20  now typically displays a message in the user interface Ul (e.g. display unit) requesting the user to enter his or her own personal identity code, i.e. a PIN code. The user enters the PIN code and, assuming it was the correct one, the mobile station  20  registers to the network  30  according to prior art technology using the user identification data of the SIM card  26  for authentication. After this, the user of the mobile station  20  can, as necessary, establish a connection to the network  30  for initiating a data connection or voice call. 
   Let us now assume that the user of the PDA device  10  (which may be the same or a different user than the user of the mobile station  20 , preferably a different user) has switched on the operating voltage to the PDA device  10 , in which case the control unit  14  of the PDA device has taken the necessary initialisation steps to start up the operation of the PDA device  10 . After the start-up, the user can use the PDA device for functions normally performed on it. When using the PDA device  10 , the user may end in a situation which requires access to the communications network  30 . The user may, for instance, want to load services to the PDA device. The services may include loading news or articles electronically from the Internet or a server of a local network (e.g. intranet, LAN (Local Area Network)). 
   In the above situation, the following action is preferably taken. Let us assume that the user of the PDA device has inserted into the PDA device the user data identification module  16  (e.g. SIM card). The user identification data contains, among other things, a network identifier given to the user of the PDA device by the network operator, which network identifier the user (subscriber) uses to register to the network, and an operator identifier identifying the network operator whose subscription the user (subscriber) has. Said network identifier of the user is preferably the IMSI code, or the like, of the user. (According to a proposal, an IMUI (International Mobile User Identity) code corresponds terminologically to the IMSI code in a third-generation network (UMTS)). It is known to a person skilled in the art that the user identification data can also comprise other parameters and information, such as encryption keys and SIM secrets. 
   The control unit  14  now generates a message which, by way of example, is called a “replace_SIM_request” message. The purpose of the “replace SIM request” message is to ask the mobile station  20  whether the mobile station  20  agrees to be used under the user identification data of another user. 
   The control unit  14  includes in the “replace_SIM_request” message the operator identifier. The operator identifier identifies the teleoperator whose subscription the user of the PDA device  10  has. As for the message in question and for other messages transmitted in the method, reference is made to  FIG. 4  which illustrates message exchange in a preferred embodiment of the invention. 
   The control unit  14  now tries to establish a short-range data transfer connection  12  to the mobile station  20 . This short-range data transfer connection  12  (e.g. a Bluetooth connection) is for security reasons to be established as an encrypted data transfer connection. When the short-range data transfer connection has, in a manner known per se, been established, the control unit  14  preferably transmits the “replace_SIM_request” to the mobile station  20  over the short-range data transfer connection in the following manner. The control unit  14  conveys the “replace_SIM_request” message to the short-range data transmission means  13 . The transmitter of the data transmission means makes the necessary modulation actions to generate a radio signal from the “replace_SIM_request” message and to transfer the radio signal to an antenna of the local link. From the antenna of the local link, the radio signal is transmitted via the local link  12  to the mobile station  20 . The radio signal being transmitted may, if necessary, have an initial synchronisation part before the actual information part so that the receiver of the mobile station can be set to receive on the correct transmission channel before the information part is transmitted. 
   The transmitted radio signal is received at the antenna of the short-range data transmission means  23  of the mobile station  20  and forwarded to the receiver of the data transmission means. The receiver demodulates the received radio-frequency signal to regenerate the “replace_SIM_request” from the radio signal. The “replace_SIM_request” message is conveyed via the control and data bus  27  to the control unit  24  of the mobile station. The control unit  24  of the mobile station examines the received “replace_SIM_request” message and takes the action it requires. In this case, the “replace_SIM_request” message asks the mobile station  20 , whether the mobile station can be used under the user identification data of another user (in this case, the user identification data of the PDA device, which resides on the SIM card  16  inserted into the PDA device  10 ). In other words, the question is whether the user identification data of the PDA device  10  can be used in the mobile station  20  for connection establishment from the mobile station  20  to the communications network  30  on behalf of the PDA device. 
   If the mobile station  20  agrees to the use of the identification data of the PDA device (this naturally requires that the mobile station has a software that supports such a replacement of identification data), the mobile station transmits to the sender of the “replace_SIM_request” message an “accept” message, which indicates to the PDA device  10  that the mobile station  20  accepts its use under the user identification data of the PDA device  10 . If the mobile station  20  rejects its use under the user identification data of the PDA device, the mobile station  20  transmits to the sender of the “replace_SIM_request” message a “reject” message, which indicates to the PDA device  10  that the mobile station  20  does not agree to the use of the identification data of the PDA device in connection establishment between the mobile station and the network  30  on behalf of the PDA device  10 . A reason for rejection may be that the mobile station simply does not support the procedure proposed by the PDA device. Alternatively, the reason may be that the mobile station has an ongoing call, or that the network operator indicated by the operator identifier in the “replace_SIM_request” message cannot be reached. The reason for rejection is included in the “reject” message. 
   Depending on the situation, the control unit  24  of the mobile station generates an “accept” or “reject” message to be transmitted via the local link  12  to the PDA device  10 . In transferring the message, the actions described in the foregoing in connection with the transmission of the “replace_SIM_request” message can be applied. In the following the transmission of the “accept” message is described. (The “reject” message is transmitted in substantially the same manner.) The control unit  24  conveys the “accept” message to the short-range data transmission means  23  of the mobile station. The transmitter of the data transmission means performs the necessary modulation actions to generate a radio signal from the “accept” message and to convey the radio signal to the antenna of the local link. From the antenna of the local link, the radio signal is transmitted via the local link  12  to the PDA device  10 . 
   The transmitted radio signal is received at the antenna of the short-range data transmission means  13  of the PDA device and is forwarded to the receiver. The receiver demodulates the received radio-frequency signal to regenerate the “accept” message from the radio signal. The “accept” message is transmitted via the control and data bus  17  to the control unit  14  of the PDA device. The control unit  14  detects that the received message is an “accept” message transmitted in response to the “replace_SIM_request” message, in which case the control unit of the PDA device generates a “SIM_contents” message which contains user identification data of the PDA device. This data comprises the network identifier, i.e. IMSI code, or the like, of the user of the PDA device, and possibly other necessary information which the SIM card  16  inserted into the PDA device contains. The purpose of the “SIM_contents” message is to transmit the necessary user identification data of the PDA device  10  to the mobile station  20  so that the mobile station  20  can register to the communications network  30  using the user identification data of the PDA device. 
   The control unit  14  conveys the “SIM_contents” message to the short-range data transmission means  13 . The transmitter of the data transmission means performs the necessary modulation actions to generate a radio signal from the “SIM_contents” message and to convey the radio signal to the antenna of the local link. From the antenna of the local link, the radio signal is transmitted via the local link  12  to the mobile station  20 . 
   The transmitted radio signal is received at the antenna of the short-range data transmission means  23  of the mobile station and is forwarded to the receiver. The receiver demodulates the received radio-frequency signal to regenerate the “SIM_contents” message from the radio signal. The “SIM_contents” message is conveyed via the control and data bus  27  to the control unit  24  of the mobile station. The control unit  24  of the mobile station examines the received “SIM_contents” message and takes the action it requires. In this case, the control unit  24  begins to register to its own network, i.e. the cellular network  30 , using the user identification data of the PDA device  10 , i.e. the IMSI code of the PDA device. The registration to the network takes place in a manner known per se. The difference is only that instead of the user identification data of the mobile station  20 , the user identification data of the PDA device  10  is used. 
   The following describes a simplified manner for the mobile station  20  to register to the network. The registration process is known per se to a person skilled in the art, so a more detailed description is not necessary herein. In the registration process, the control unit  24  of the mobile station generates an “authentication” message which contains the IMSI code, or the like, of the user of the PDA device  10 . The control unit  24  conveys the “authentication” message via the control and data bus  29  to the radio part  33 . The radio part comprises a transceiver, which performs the necessary modulation actions to generate a radio signal from the “authentication” message and to convey the radio signal to the antenna of the radio part  23 . From the antenna of the radio part, the radio signal is transmitted via the cellular network connection  32  to the network  30 . As earlier noted, the network is preferably a cellular network, such the GSM or UMTS network. 
   The transmitted radio signal is received at the network  30  where it is demodulated to regenerate the “authentication” message from the radio-frequency signal. The network processes the “authentication” message and takes the action it requires. In this case, the network  30  examines whether it can accept the registration to the network  30  of the subscriber identified by the user identification data (IMSI code or the like). This is typically done by a challenge-response procedure. In it, the network  30  generates a random number RAND and transmits it as a challenge over the cellular network connection  32  to the mobile station  20  which, in turn, transmits the random number RAND over the local link  12  to the PDA device. The control unit of the PDA device receives the random number RAND and transfers it over the second control and data bus  18  to the SIM card  16  in the slot of the reader  15 . The processor of the SIM card generates a response SRES on the basis of the random number RAND and a specific SIM secret Ki and using a particular algorithm, and the response is transmitted from the SIM card  16  to the control unit  14  of the PDA device. The control unit  14  transmits the response SRES over the local link  12  to the mobile station  20  from which it is transmitted on to the network  30  via the cellular network connection  32 . The network  30  which knows said SIM secret Ki, generates, on its part, a SRES using the same algorithm as the processor of the SIM card  16 . When the network  30  receives the response SRES via the mobile station  20  from the SIM card  16  of the PDA device, the network  30  compares the SRES that it has generated by itself to the SRES received from the SIM card  16  of the PDA device. If the SRES generated by the network matches the SRES received from the SIM card  16 , the network  30  accepts the registration of the mobile station  20  to the network using the user identification data of the PDA device  10 . 
   If the network  30  accepts the registration of the subscriber (the user/subscriber identified by the IMSI code of the SIM card of the PDA device) to the network, an “accept” message is transmitted from the network to the sender of the “authentication” message to indicate to the wireless communication device that the network accepts the registration of the subscriber to the network. If the network rejects the registration, a “reject” message is transmitted from the network to the sender of the “authentication” message to indicate to the wireless communication device that the network  30  does not accept the registration of the subscriber to the network. The reason for rejection may be that the subscriber in question simply does not have permission to register to the network of the network operator in question. The reason for rejection is included in the “reject” message. 
   Even though the messages associated with the registration process have been shown in a simplified manner with two messages in  FIG. 4 , it is clear to a person skilled in the art that network registration can be a multistage process, as already alluded in connection with the description of the challenge-response procedure. The messages that in the registration process are transferred between the wireless communication device and the network may differ from what is stated above, but are known to a person skilled in the art. 
   For the network, it is irrelevant per se, whether the user of the mobile station  20  or the user of the PDA device  10  registers to the network with the mobile station  20 . The registration process is similar for the network in both cases. In most cases, it is necessary that the mobile station  20  using the user identification information of its own SIM card  26  de-registers from the network  30  in a manner known per se before registering to the network using the user identification data of the PDA device. 
   Let us now examine the reception of the “accept” message transmitted in response to the “authentication” message in the mobile station  20 . (A “reject” message is received in substantially the same manner.) The mobile station  20  receives a radio-frequency signal transmitted by the network  30  and containing the “accept” message at the antenna of the radio part  33 . From the antenna, the radio signal is conveyed to the receiver of the radio part  33 , which demodulates the received radio-frequency signal to regenerate the “accept” message from the radio signal. The “accept” message is transmitted via the control and data bus  29  to the control unit  24  which identifies the “accept” message as a response transmitted to the “authentication” message. The “accept” message indicates to the control unit that the registration to the network  30  was successful. The mobile station  20  informs the PDA device  10  of this. This takes place in such a manner that the control unit  24  transmits the “accept” message received from the network on to the PDA device. The transmission occurs over the local link  12  in a respective way as described in the foregoing description. The control unit  24  thus conveys the “accept” message to the short-range data transmission means  23 . The transmitter of the data transmission means performs the necessary modulation actions to generate a radio signal from the “accept” message and to convey the radio signal to the antenna of the local link. From the antenna of the local link, the radio signal is transmitted over the local link  12  to the PDA device  10 . 
   The transmitted radio signal is received at the antenna of the short-range data transmission means  13  of the PDA device and is conveyed to the receiver of the PDA device data transmission means. The receiver demodulates the received radio-frequency signal to regenerate the “accept” message from the radio-frequency signal. The “accept” message is conveyed via the control and data bus  17  to the control unit  14  of the PDA device. The control unit  14  detects that the received message is an “accept” message transmitted as an indirect response to the “SIM_contents” message. The “accept” message indicates to the PDA device that the mobile station  20  has succeeded in registering to the network using the data on the SIM card  16  of the PDA device. 
   The mobile station  20  stores into its memory information on the fact that the registration to the network  30  was done using the user identification data of the PDA device. On the basis of this information, the mobile station can in a connection established later forward to the PDA device  10  information, such as data, received from the network  30 . 
   Depending on what services the user of the PDA device  10  has subscribed to his or her SIM card  16 , the PDA device  10  can establish a circuit-switched connection (e.g. a data call or an HSCSD (High Speed Circuit Switched Data) connection) and/or a packet-switched connection (e.g. a GPRS (General Packet Radio Service) connection) to the network  30  via the mobile station  20 . 
   If the PDA device  10  wants to setup a data call connection, for instance, this is performed as follows. The control unit  14  of the PDA device first generates an “initiate_call” message. The address of the receiver, for instance a telephone number or IP (Internet Protocol) number, is attached to the “initiate_call” message. It is clear to a person skilled in the art that the “initiate_call” message may also comprise lots of other information, for instance user identification data of the PDA device  10 , such as the IMSI code. 
   The control unit  14  conveys the “initiate_call” message to the short-range data transmission means  13 . The transmitter of the data transmission means performs the necessary modulation actions to generate a radio signal from the “initiate_call” message and to convey the radio signal to an antenna of the local link. From the antenna of the local link, the radio signal is transmitted via the local link  12  to the mobile station  20 . 
   The transmitted radio signal is received at the antenna of the short-range data transmission means  23  of the mobile station and is forwarded to the receiver. The receiver demodulates the received radio-frequency signal to regenerate the “initiate_call” message from the radio signal. The “initiate_call” message is conveyed via the control and data bus  27  to the control unit  24  of the mobile station. The control unit  24  of the mobile station examines the received “initiate_call” message and takes the action it requires. In this case, the “initiate_call” message has been transmitted to set up a data call connection. On the basis of the information in the “initiate_call” message, the control unit  24  generates a prior-art call set-up request, i.e. a “call_setup” message to set up a data call. To identify the user, the IMSI code, or the like, of the user of the PDA device  10  is preferably attached to the “call_setup” message. The mobile station  20  transmits the “call_setup” message via the antenna of its radio part  33  to the network  30 . The network either accepts or rejects the call set-up request. If the network  30  accepts the call set-up request, it transmits an “accept” message to the mobile station  20  in response to the “call_setup” message. If the network  30  rejects the call set-up request (e.g. too high a load in the network), it transmits a “reject” message to the mobile station  20  in response to the “call_setup” message. The mobile station  20  receives the message (“accept” or “reject”) transmitted by the network  30  at the antenna of its radio part  33  and forwards the message to the receiver and from it, after demodulation actions, further to the control unit  24 . The mobile station  20  transmits the message received from the network further via the local link to the PDA device  10  to let the PDA device know whether the call set-up request was accepted or rejected. It is clear to a person skilled in the art that the messages transmitted between the mobile station  20  and the network  30  in setting up a call may differ from what is stated above, call set-up between the mobile station  20  and the network  30  is known to a person skilled in the art. The essential thing is that the call is set up between the mobile station  20  and the network  30  using the user identification data of the PDA device  10 , such as the IMSI code or the like. The mobile station  20  routes the call to the PDA device  10  over the local link  12 . 
   This way, the PDA device  10  can set up a data call connection from the mobile station  20  to a number from which a desired information content, such as a piece of news or article, can be downloaded, and download it to its memory via the mobile station  20 . In practice, the PDA device  10  can, for instance, generate a WAP WSP (Wireless Session Protocol) GET request and transmit it via the local link  12  to the mobile station  20 . The mobile station  20  receives the WAP WSP GET request and transmits it on via the data call connection to a WAP gateway (not shown) in the network  30 . The WAP gateway fetches in a manner known per se the information content desired by the PDA device from the database of the service provider, which can, for instance, reside on an Internet server or a server of a local network, and transmits the information content via the network  30  over the data call connection to the mobile station  20 . The mobile station receives the information content and transmits it on to the PDA device via the local link  12 . Alternatively, the connection  32  between the mobile station  20  and the network  30  can be some other data connection than a data call connection, such as a GPRS connection or another data connection supported by the WAP protocol. 
   The invention is preferably implemented between the PDA device  10  and the mobile station  20  by using an application-specific protocol, herein referred to as an AIRC (Access Identifier Replacement Control) protocol. The above messages “replace_SIM_request”, “SIM_contents”, “initiate_call”, “accept” and “reject” are all messages according to the AIRC protocol. The AIRC protocol can be implemented as a separate module in the PDA device and a separate module in the mobile station in such a manner that the AIRC modules are coupled to the control units of the devices. Alternatively, the AIRC protocol can be integrated to the rest of the PDA device and mobile station software. 
     FIG. 3  illustrates in a simplified manner a data transfer method in a preferred embodiment of the invention. Communication between the PDA device  10  and the mobile station  20  takes place over a local link. In the examplary case of  FIG. 3 , the local link is a Bluetooth link. The AIRC protocol layer is on top of the Bluetooth protocol layer BT in both the PDA device and the mobile station. The AIRC protocol layer of the PDA device communicates with the AIRC protocol layer of the mobile station. The messages of the AIRC layer are transferred with the aid of the Bluetooth layer BT. GSM and/or UMTS protocols are used in the communication between the mobile station  20  and the network  30 . 
   The purpose of the AIRC protocol is to make the PDA device  10  and the mobile station  20  understand each other. The AIRC protocol thus creates a set of rules for message exchange between the PDA device and the mobile station so that the PDA device and the mobile station can generate the messages according to the invention and process correctly the messages they receive from each other. 
   In addition to the messages described above, other messages can be implemented using the AIRC protocol. For instance, if no information has been transmitted for a long time over the Bluetooth link acting as the local link  12 , the mobile station  20  generates a “PDA_SIM_alive” message to find out from the PDA device  10 , if it still needs the connection  32  to the network. In practice, the mobile station transmits the “PDA_SIM_alive” message over the Bluetooth link when a pre-defined timer in the mobile station is expired after a long idle time in the Bluetooth connection. If the PDA device does not respond to the “PDA_SIM_alive” message with an “acknowledgement” message, the mobile station  20  decides that the connection  32  to the network is no longer needed and disconnects it and can again start to use its own SIM card (registers to the network with its own SIM card  26 ). If the PDA device responds to the “PDA_SIM_alive” message with an “acknowledgement” message, the mobile station deduces that the connection  32  is still needed. 
   In a normal case, the PDA device  10  transmits a “SIM_replace_end” message over the local link  12  to the mobile station to indicate to the mobile station  20  that the data connection  32  from the terminal to the network  30  is no longer needed, in which case the mobile station disconnects the connection to the network and can again start to use its own SIM card  26 . 
     FIG. 5  illustrates another embodiment of the invention. In this embodiment, the SIM card  26  of the mobile station  20  is the SIM card of an operator  1 , and the SIM card  16  of the PDA device  10  is the SIM card of an operator  2 . The operators  1  and  2  are different teleoperators. Let us assume that a service provider  1  has made an agreement with the operator  1 , in which case a content database  51  (content database  1 ) maintained by the service provider  1  is connected to a network  30 A (network  1 ) operated by the operator  1 . Let us also assume that a service provider  2  has made an agreement with the operator  2 , in which case a content database  52  (content database  2 ) maintained by the service provider  2  is connected to a network  30 B (network  2 ) operated by the operator  2 . The content databases  51  to  52  are databases from which information contents, such as electronic articles or pages of an electronic newspaper or book, can be fetched to the PDA device. The mobile station  20  can, as described earlier in this description, establish a connection to the network  30 B of the operator  2  using the user identification data of the PDA device  10  in the SIM card  16  of the PDA device, and fetch one or more information contents from the content database  52  to the PDA device via the mobile station. However, if the PDA device wants to fetch an information content from the content database  51  connected to the network  30 A of another operator (operator  1 ), the mobile station  20  can de-register from the network  30 B operated by the operator  2  and register to the network  30 A operated by the operator  1  with its own SIM card. Further, the mobile station can fetch an information content from the content database  51  connected to the network  30 A and transfer the information content over the Bluetooth connection  12  to the PDA device. This way, an information content can be fetched to the PDA device  10  regardless of which operator each service provider has made an agreement with. 
   A person skilled in the art understands that the names used for different messages and the AIRC protocol in this description are for example only, and they are mainly used for illustrative purposes herein. The implementation of the invention is thus not restricted to the use of these specific messages. 
   This description describes the implementation and embodiments of the invention by means of examples. It is obvious to a person skilled in the art that the invention is not restricted to the details of the embodiments described in the foregoing and that the invention can be implemented in other ways without departing from the characteristics of the invention. The presented embodiments should be considered illustrative, but not restrictive. The implementation and use of the invention are thus restricted only by the attached claims. Therefore, different alternative implementations of the invention, including equivalent implementations, defined by the claims fall within the scope of the invention.