It's called Modem::Vgetty. I've only just purchased a voicemodem (since I'm on cable) for trying some telephony tricks with this module, so I can't tell you much about the quality yet... from the documentation, though, it looks pretty complete.

Note also Modem::VBox, which seems to be an attempt at a prettier Modem::Vgetty. The documentation is somewhat less than complete, however. :-)