This certification saves time and money, not to mention your sanity, compared to designing your own modem and getting it approved. Modems are rather power-hungry beasts when they're actually doing something. However, all the latest models include automatic power-down modes that reduce power significantly when the modem is idle. If your app is power-consumption critical, it's probably best to control the modem's power supply externally and just shut it completely off between uses. Making things easy for designers, all the units rely on a simple asynchronous TTL, serial-host connection, and the familiar AT commands.
All options offer an audio output for driving an amp and speaker.
These days, software modems are all the rage. AltoCom offers a virtual line card of software modems up to and including a V.90 56-kbps one with all the trimmings. It has extensions for fax, simultaneous voice and data, speaker phone, voice mail, and even video conferencing. Gao Research and Consulting offers a lean and mean V.22bis 2400-kbps soft modem. To cut the memory footprint, the software is written in assembly language for the Analog Devices' ADSP-21 xx and Texas Instruments' TI C54 x .