International Mobile Subscriber Identity (IMSI)
An International Mobile Subscriber Identity or IMSI ) is a unique number associated with all GSM and UMTS network mobile phone users. It is stored in the SIM inside the phone and is sent by the phone to the network. It is also used to acquire other details of the mobile in the Home Location Register (HLR) or as locally copied in the Visitor Location Register. In order to avoid the subscriber being identified and tracked by eavesdroppers on the radio interface, the IMSI is sent as rarely as possible and a randomly-generated TMSI is sent instead.
An IMSI is usually 15 digits long, but can be shorter (for example MTN South Africa's old IMSIs that are still being used in the market are 14 digits). The first 3 digits are the Mobile Country Code (MCC), and is followed by the Mobile Network Code (MNC), either 2 digits (Europeanstandard) or 3 digits (North American standard). The remaining digits are the mobile station identification number (MSIN) within the network's customer base.
MCC 429 Nepal
MNC 01 Nepal Telecom
MCC 310 USA
MNC 150 AT&T