Call Number Identification in GSM

    If an adversary knows certain information (IMSI, IMEI, MSISDN) about the subscriber or a mobile phone, he can then identify individual phone calls, although this does require extensive technical effort.

    With the aid of IMEI it is possible to selectively filter calls out from the datastream on the mobile network radio relay links. Calls can also be identified in the public telephone landline network, for which knowledge of the subscriber call number is necessary. With the appropriate interception equipment, the IMSI and IMEI can be ascertained directly on the radio link between mobile phone and base station.

     An insider, either at the network provider's or, for example, in a company that extracts work or private telephone numbers from telephone lists, could identify the call number MSISDN by working out the relationship between IMSI, IMEI and MSISDN in the relevant database.