A 1200 bauds modem based on an Arduino Nano mainly for APRS amateur radio.
nonaprs.fzz is the Fritzing file, the associated gerber files are in gerber_export directory.
This is not the best PCB design but it works perfectly, I'm using it for an iPhone project I'm working on.
You can order it on OSHPark.
You can program the modem with the library from Mark