Abstract: A modem is equipped with both a conventional telephone line interface for attaching to a wired telephone jack and a special interface for connecting to a cellular telephone. The modem interacts with the cellular telephone in accordance with a special protocol, wherein signals of the protocol are derived directly from the conventional modem signals used to interact with the wired telephone jack. No high voltage signals need pass between the modem and cellular telephone. Substitution of the cellular telephone for the wired telephone jack is transparent to the software used to operate the modem. Aside from a connection cable, no special hardware is required between the cellular telephone and modem.