Modem is a class 2.0 fax mode. Works better than class 2, if both are available, because its better standardized. Known to work with USR, ZyXEL 1496 and 2864 series, and ELSA modems. To my knowledge, there are no such modems available yet, but supporting them will be easy as class 2.1 is very similar to class 2.0. Modem can do class 1 fax conforming to ITU T.31 standard.
Some modems have a very peculiar interpretation of the fax standards.
Usually you won't need this option, because those modems really needing it are auto-detected and handled properly anyway. Tells mgetty the chat sequence to use for initializing the modem. This ordering was chosen because UUCP does it this way, and I wanted to avoid confusion here. In some cases, the modem can get stuck in a mode where it won't react to a simple AT command. Usually this happens because the modem is set to ignore a DTR drop and still has a data connection to the other side.