IMSI

international mobile subscriber identity

A unique number associated with each mobile phone user. It is stored in the SIM inside the phone and is sent by the phone to the network. It is primarily intended for obtaining information on the use of the PLMN by subscribers. It is also used for other functions, such as to compute the Paging Occasions (PO) in LTE. See 3GPP TS22.016 and TS23.003.*