USIM - definition
USIM stands for Universal Subscriber Identity Module which is specially designed to serve with 3G or UMTS networks. User can make video call using USIM in a 3G device under a 3G coverage area. Also, the security algorithm is much higher in USIM. An USIM can provide storage for phone book up to 256K where a regular SIM can store up to 32K and 64K at best.