In mobile networks, location area identity (LAI) is a unique identifier assigned to each location area of a public land mobile network (PLMN).
[1] This internationally unique identifier is used for location updating of mobile subscribers.
It is composed of a three decimal digit mobile country code (MCC), a two to three digit mobile network code (MNC) that identifies a Subscriber Module Public Land Mobile Network (SM PLMN) in that country, and a location area code (LAC) which is a 16 bit number with two special values, thereby allowing 65534 location areas within one GSM PLMN.
A mobile station (e.g. cell phone) recognizes the LAI and stores it in the SIM Card.
This allows the provider to locate the mobile station in case of an incoming call.