Oh, I love this.

Throwing this in the “fun retro internet” pile alongside https://neocities.org/

telnet or ssh (usually telnet)

If you’re connecting from a modern computer, you just get a telnet client that does the appropriate code pages/ANSI/zmodem/etc. If you’re connecting from a real vintage computer, you get a little dongle that appears to be a modem (and often accepts AT commands, including fake phone numbers), but secretly connects to WiFi and relays through a telnet connection.

Some BBSes do still have landlines, and there’s the occasional ham radio BBS, but 99.999% of it is through IP-based telnet or ssh these days.

ssh and/or telnet.

Sadly most people CAN’T connect through dial-up, even if both parties have all the equipment. A lot of telcos have redone their entire network in VoIP stuff (with heavy compression) which makes it hard to keep a connection even at 300.