Is there a softmodem driver package for Linux?

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!