I'd like to run an old-school BBS that can be dialed into over a real phone line. Unfortunately, I don't currently have the necessary hardware to do so. I had the idea of purchasing a VPS and then using an SIP softphone and some BBS software to accomplish the same task. The only problem is that I can't find anything that emulates a modem. I'm aware of a program called minimodem, but that seems to only work for FSK and doesn't support any kind of handshaking. Ideally the program would create a virtual serial port and take input from / output to a sound device. Does anyone know of any software like this? Thanks!
There is the Linmodem project, made by (who else) Fabrice Bellard. Unfortunately, it is more of a proof-of-concept than a working, ready-to-use driver, and it has been abandoned in that state in 2000. It barely contains incomplete implementations of four Hayes/AT commands and the V.34 protocol, and has not been ported to the modern Linux audio stack (ALSA), or even the Unix 98 pseudo-terminal interface. Even compiling it as it is under a modern system requires some light patching (mostly adding missing
extern specifiers and re-ordering compiler flags).
Nevertheless, for someone willing to spend some time on developing a software modem, this might be a good starting point.
There are people around who are running BBS on dialup and emulated lines.
The answers given in this related question (which is C64-specific) give some sources of software that may be useful to you.
In particular The BBS Corner. However, the site hasn't been updated for a while so you may have to dig around a little.
Not terribly authentic if it is all simulated like that. But more importantly, there is the complication that while much of a modem's capabilities can be handled by software instead of hardware (personally I never found that soft-modems worked very well, but that's a separate issue), the sound card input/output is not going to have the on-off capability and, I suspect (but could be wrong) ring-tone detection needed for a functioning modem. Remember acoustic couplers? They relied on a human being for ring-tone detection and placing on/off hook.
The good news is that eBay has plenty of modems available, many from major brands (e.g., US Robotics), for under $ 20, including some still in their shrink wrapped boxes.