A method providing communication between an MSC and a mobile terminal in a wireless communications system including using the 10 digit MIN identifier for identifying the mobile terminal in all messages requiring a mobile terminal identifier sent from the MSC via a base station to the mobile terminal and using the 15 digit MIN-based IMSI identifier for identifying the mobile terminal in all messages requiring a mobile terminal identifier sent from the mobile terminal via the base station to the MSC. The method can also include deploying the use of 15 digit MIN-based IMSI identifiers in one MSC at a time. The invention also includes a system for providing mobile terminal identification information in a wireless system. The system includes a mobile terminal capable of receiving and responding to messages using a 10 digit MIN for identifying the mobile terminal and sending messages having a MIN-based IMSI identifier for identifying the mobile terminal. The system also includes an MSC capable of receiving and processing messages from the mobile terminal having the MIN-based IMSI identifier and sending messages to the mobile terminal using the 10 digit MIN identifier.