A method for calculating a call expense of a terminal, comprising: after receiving, by a cost calculating module, a call attribute, reading, by the cost calculating module, a billing rule and an account balance in a cost file, calculating, by the cost calculating module, a call expense and a current account balance, and then updating, by the cost calculating module, the account balance in the cost file; and updating the billing rule and/or the account balance in the cost file in time through an Over-The-Air, OTA, short message, wherein the cost file is stored in a Subscriber Identity Module, SIM, card used by the terminal, wherein the cost calculating module is located in the SIM card and/or in the terminal, wherein the calculating, by the cost calculating module, a call expense and a current account balance comprises: searching, by the cost calculating module, billing rules in the cost file for a billing rule that corresponds to a call type and a roaming indicator contained in the call attribute; and when an appropriate billing rule is found, calculating, by the cost calculating module, the call expense and the current account balance using the appropriate billing rule found, wherein the current account balance is calculated by the cost calculating module as: current account balance = original account balance - call expense, wherein the original account balance is an account balance in the cost file read from the SIM card, wherein the updating the billing rule and/or the account balance in the cost file in time through an OTA short message comprises: when there is a billing-rule change, and/or when there is an account-balance change due to account-recharging by a subscriber, compiling, by an OTA control centre, a latest billing rule and/or a latest account balance into the OTA short message, and sending, by the OTA control centre, the OTA short message to the terminal that uses the SIM card; forwarding, by the terminal, the received OTA short message to the SIM card; and updating, by the SIM card, the billing rule and/or the account balance in the cost file according to the OTA short message, and saving, by the SIM card, the cost file. after receiving, by a cost calculating module, a call attribute, reading, by the cost calculating module, a billing rule and an account balance in a cost file, calculating, by the cost calculating module, a call expense and a current account balance, and then updating, by the cost calculating module, the account balance in the cost file; and updating the billing rule and/or the account balance in the cost file in time through an Over-The-Air, OTA, short message, wherein the cost file is stored in a Subscriber Identity Module, SIM, card used by the terminal, wherein the cost calculating module is located in the SIM card and/or in the terminal, wherein the calculating, by the cost calculating module, a call expense and a current account balance comprises: searching, by the cost calculating module, billing rules in the cost file for a billing rule that corresponds to a call type and a roaming indicator contained in the call attribute; and when an appropriate billing rule is found, calculating, by the cost calculating module, the call expense and the current account balance using the appropriate billing rule found, wherein the current account balance is calculated by the cost calculating module as: current account balance = original account balance - call expense, wherein the original account balance is an account balance in the cost file read from the SIM card, wherein the updating the billing rule and/or the account balance in the cost file in time through an OTA short message comprises: when there is a billing-rule change, and/or when there is an account-balance change due to account-recharging by a subscriber, compiling, by an OTA control centre, a latest billing rule and/or a latest account balance into the OTA short message, and sending, by the OTA control centre, the OTA short message to the terminal that uses the SIM card; forwarding, by the terminal, the received OTA short message to the SIM card; and updating, by the SIM card, the billing rule and/or the account balance in the cost file according to the OTA short message, and saving, by the SIM card, the cost file.