Not much.

It uses GSM, which can be listened to by a RTL-SDR or any other software defined radio.

http://www.rtl-sdr.com/receiving-decoding-decrypting-gsm-sig...

Not at all - it uses closed-source/closed-hardware baseband module, so no one really knows what is happening inside. This project is more of custom board, keyboard, display, OS, UX around readily available solution.

No successful or legal opensource/openhardware solutions exist right now :/ This was one of main problems with OpenMoko opensource phone.