It would be great if we had a modem bank for dial-up implemented as SIP clients, so we don't need a bunch of physical modems on the server side. Here's a couple of links.

• https://github.com/AonCyberLabs/D-Modem
  • https://github.com/FOSS-Archive/D-Modem/pull/1
• https://vocal.com/voip/sip-analog-modem-server-sams/
• https://bellard.org/linmodem/