A method of enabling personalised shared mobile phone usage using Unstructured Supplementary Service Data, USSD messages, the method comprising the steps of: the owner of the mobile phone enabling shared mobile phone usage mode by entering a USSD message string; USSD gateway routing the USSD message string to system server; the system server interacting with Mobile Services Switching Centre, MSC, and temporarily disabling access to services from the mobile phone and billing of said services to the owner's account; the owner sharing the mobile phone with a subscriber; the subscriber requesting access to the subscriber's prepaid or postpaid account from the mobile phone using a second USSD message string, said second USSD message string including the subscriber's personal phone number; the system server sending to the mobile phone a request for an access password; the subscriber entering the access password; the system server authenticating the subscriber and sending a USSD personalised menu to the mobile phone; the system server interacting with the MSC to ensure that the shared mobile phone and Subscriber Identity Module, SIM, are enabled to allow phone services and that all charges will be debited against the subscriber's own prepaid or post-paid account during the USSD session; the system server enabling the subscriber to make mobile telecommunication phone calls from the shared mobile phone by allowing the subscriber to enter a number to be dialled using the USSD personalised menu; once the subscriber requests a call, the system server connecting the number to be dialled by interacting with the MSC; the system server decrementing the subscriber's prepaid account balance in real time depending on network call rates until the USSD session is closed by the subscriber, or prepaid account credit is expired. the owner of the mobile phone enabling shared mobile phone usage mode by entering a USSD message string; USSD gateway routing the USSD message string to system server; the system server interacting with Mobile Services Switching Centre, MSC, and temporarily disabling access to services from the mobile phone and billing of said services to the owner's account; the owner sharing the mobile phone with a subscriber; the subscriber requesting access to the subscriber's prepaid or postpaid account from the mobile phone using a second USSD message string, said second USSD message string including the subscriber's personal phone number; the system server sending to the mobile phone a request for an access password; the subscriber entering the access password; the system server authenticating the subscriber and sending a USSD personalised menu to the mobile phone; the system server interacting with the MSC to ensure that the shared mobile phone and Subscriber Identity Module, SIM, are enabled to allow phone services and that all charges will be debited against the subscriber's own prepaid or post-paid account during the USSD session; the system server enabling the subscriber to make mobile telecommunication phone calls from the shared mobile phone by allowing the subscriber to enter a number to be dialled using the USSD personalised menu; once the subscriber requests a call, the system server connecting the number to be dialled by interacting with the MSC; the system server decrementing the subscriber's prepaid account balance in real time depending on network call rates until the USSD session is closed by the subscriber, or prepaid account credit is expired.