This paper discusses alternatives for high-speed data transfer between the host and Subscriber Identity Module (SIM) or Universal SIM (USIM) cards typically used with GSM mobile handsets. It focuses on a comparison of the Universal Serial Bus (USB) and the Multimedia Card (MMC) interfaces as candidates for such an interface. Either of these high-speed interfaces may be implemented in addition to the current ISO 7816 interface; in the future, they may replace (or emulate) ISO 7816 functionality as the only smartcard interfaces.