Encrypted GSM phone

Hi, I have been just wondering... would it be possible to use your project as a base for DIY encrypted cellphone? My idea is that if I could get hold to output data after voice is encoded by GSM EFR codec, I might just easily encrypt this digital stream using AES128 and build trully encrypted cellphone. Where does actual "analog voice from microphone to digital data" conversion happends? In a layer1 that runs in a chip, or layer23 that runs on a PC? If it would be in layer23, encrypting a data stream with AES 128 whould be doable, am I missing something? Thanks Marek -- S pozdravem / Best regards Marek Stopka Kontakty / Contacts Mobil/Cell phone:+420 608 149 955 WEB: www.stopkaconsulting.eu