Abstract: A modem configurable to operate in a normal mode to perform data communications on the Public Switched Telephone Network (PSTN) additionally configurable to operate in a duplex speakerphone mode. Preferably, the modem is a Personal Computer Memory Card Industry Association (PCMCIA) card for insertion into a connector in a portable computer. The computer includes a sound system with associated microphone and speaker that is incorporated in or associated with the portable computer as the audio input and output for the speakerphone operation. The modem incorporates an interface which allows digitized audio samples from the coder portion of a voice coder-decoder (CODEC) on the modem to be communicated to the computer and digitized audio samples from the computer's sound system to be communicated to the decoder portion of the modem's CODEC. The interface is configured in a manner which is transparent to the modem's normal data communications functions, i.e.