SIM :
A Subscriber Identity Module (SIM) is a stripped-down smart card containing information about the identity of a cell-phone subscriber, and subscriber authentication and service information. Because the SIM uniquely identifies the subscriber and is portable among handsets, the user can move it from one kind of phone to another, facilitating international roaming.
SMS :
Short Message Service (SMS) is a point-to-point service similar to paging for
sending text messages of up to 160 characters to mobile phones.