What Does Direct-Connect Modem Mean?
A direct-connect modem is a network device that is connected directly to telephone lines without the use of an acoustic coupler. Nearly all modern modems are direct-connect modems in that they have no acoustic coupler.
Techopedia Explains Direct-Connect Modem
Some modems with acoustic couplers are still used by world travelers where electrical connections to the telephone system are illegal or not available. Moreover, many models of telecommunications devices for the deaf (TDD) still have acoustic couplers built-in to them. This is intended to give the user universal use with pay phones.