AT&T MERLIN LEGEND System Reference Manual page 534

Hardware
5-28 Adapters
When a modem is connected to an analog multiline telephone using a GPA,
data calls and voice calls are dialed by using the telephone dialpad. The
modem and telephone do not operate independently features assigned to the
telephone also apply to the analog data station (modem and associated data
terminal).
Modem Features
The modem used in an analog data station (and not in a modem pool) provides
the following features:
dialing or ending asynchronous data calls from the keyboard when
connected using a basic telephone station jack on a 012 module or when
connected to an MLX telephone using an MFM
autobaud (also called data metering or speed matching) - the ability to
adjust the speed of transmission to match the speed of the data terminal
being called
automatic or manual answering of incoming data calls
self-test and maintenance procedures
ability to set data options for the call on the keyboard and, if necessary,
change the options without dropping the call