A SIMM System and method is provided that supports many Mobile Subscriber Integrated Service Digital Network (MSISDN) numbers on a mobile device. The mobile device includes one Subscriber Identity Module (SIM) and one International Mobile Subscriber Identity (IMSI). The SIMM system includes at least one signal gateway that supports the use of numerous MSISDN numbers by the mobile device. The signal gateway couples among components of the public mobile networks to which the MSISDN numbers correspond. The signal gateway connects calls between the mobile device and a first public mobile network using a first MSISDN where, for example, the first public mobile network is in a first country. Likewise, the signal gateway connects calls between the mobile device and a second public mobile network using a second MSISDN where, for example, the second public mobile network is in a second country.