Allow users to make prepaid calls on their cellular phones. They come in two varieties: the country-specific SIM (Subscriber Identity Module) card, a smart card that stores the key identifying a mobile phone subscriber within a specific country; and the international SIM card, which allows smart card holders to send and receive calls from around the world on their cellular phones with one prepaid card. The international prepaid SIM card gives cardholders the convenience of global roaming and one phone number. Both types are also available in a nonprepaid variety; here, phone calls are billed to clients in much the same way that a regular telephone service provider bills clients placing long-distance telephone calls.

See Also: Smart Card.