The first forum I ran used phpBB2. It was so simple and easy to use, I do miss the days of basic forums like that. I also never noticed any sort of performance issues, even with on occasions thousands of hourly visitors. That forum launched in around 2007-08 or so, and closed in 2012-13 time. From then on, I tended to lean mainly towards MyBB, as the availability of themes, plugins and modifications was so much better than phpBB3. phpBB3 I also found unnecessarily complicated, and the fact they didn't offer a plugin/modification installer natively sucked. (with MyBB, you could install plugins and setup settings in a matter of 5 minutes, with phpBB3, a similar plugin setup could take an hour or more)
You know that you could turn off the dial up noises, right? Most modems didn't need to run it back through the soundcard - indeed for years I didn't have that noise going on because I'd turned it off.
ATM0 was probably your friend. (If you're curious, most old school modems followed a standardish set of commands called the Hayes command set, for more information read something like http://losno.lisa.univ-paris-diderot.fr/Electronik/Hayes.htm - AT was the command to say commands followed, M was the speaker control.)
The first software I used was phpBB 3, though it was hosted through Forumotion. It's the worst one to start with IMO, since the permissions can be confusing to those who are new to owning forums.