If you have AppleTalk Remote Access installed on your Macintosh, and you are having a problem establishing an outgoing connection when sending a fax, trying to log onto an online service and so on, check the AppleTalk Remote Access Setup and ensure that the "Answer Calls" option is turned off.
AppleTalk Remote Access has priority over the modem. If the modem is set to answer an incoming call in the AppleTalk Remote Access Setup, the modem port is disabled from placing an outgoing call.