There are off the shelf dev boards for many of the specific functions the device will carry out. Once the dev board based prototype works, I can lay out a dedicated PCB to allow for a smaller form factor.

The first key component choice is how to hook the base station up to a telephone line. After doing a bit of research, it was quite clear you can't legally just make a home-brew circuit and wire it straight to your telephone line. In the US, the FCC requires a registration for any device plugged into a telephone line. And with good reason – something feeding the wrong voltage into the wires can cause serious damage to the switching equipment at the other end.

This doesn't put home-brew telephone equipment out of reach, though. Cermetek sells a number of modules that are pre-registered with the FCC, and the FCC considers their module to be the device plugged into the phone line. This lets you build whatever electronics upstream you need, without having to jump through hoops to get it tested and registered. They're not particularly cheap, but it beats paying a fine. So this project will use a Cermetek CH1840 telephone line interface module.

Next is the choice of microcontroller board. For simplicity, I will be using the same board in the base and the handset. Since I don't have very much experience with embedded microcontroller code, good support and existing audio libraries are highly desirable. Although the Raspberry Pi 3 has both built in audio and WiFi capability, the hardware design is not open enough to allow taking the design from a dev board to a dedicated PCB, so that rules it out. While the Arduino family is one of the best documented and supported platforms, it does not offer much for audio capabilites. So the most reasonable choice for microcontroller board looks like it will be a Teensy 3.2.

After that, the Teensy has its own dedicated audio adapter. To connect the two Teensys wirelessly, the prototype will use HUZZAH ESP8266 modules. I'll see if that provides adequate range.