How do I use a modem with a mac on a tcp ip network?

One FirstClass feature made the system particularly popular. The server was multithreaded, and the client added a thread for every window. This meant that the user could open multiple messages at the same time, while uploading and downloading in the background. Whereas most systems indirectly encouraged users to simply "leech" files and then leave, users waiting for downloads on FirstClass had an entire modem channel free for uploading or writing. And write they did; generally the average user posted about three times as many messages as on traditional command-line based systems. Even with a single phone line and a tiny user base, the system soon had message volumes approaching that of major commercial services such as Canada Remote Systems and even entire networks such as FidoNet. The GUI also offered access to users who would normally never call a BBS system; the user base was about half women in a time where 5% might be more common, and represented a wide range of users and ages.