It’s featured in an episode of Adrian’s Digital Basement if you want to see someone build one and try it out.

https://youtu.be/De5ufcDueRU?si=cY7kKrlY8slFIM3G

I did something similar with a Raspberry Pi inside as US Robotics Sportster 14400 Modem, running pppd over serial to give an old Mac internet access. I also rigged it to play the modem handshake when starting the PPP session.