User Identity Module(UIM) for IMT-2000 systems

User Identity Module(UIM) is widely deployed in GSM(Global System for Mobile communications), Known as SIM(Subscriber Identity Module). We can expect that UIM will be also available for ANSI based third generation systems. Removable User Identity Module(R-UIM) is UIM for ANSI based third generation systems and Universal Subscriber Identity Module(USIM) is UIM for GSM based third generation systems. This paper identifies differences between R-UIM and USIM and studies global roaming in IMT-2000 systems.