'open GPRS protocol'?
There is no such thing. While you can crack it if you have mad skills, resources and high tech equipment, communication tech comes with encryption, esp CDMA (W-CDMA aka 3G), thats why you have those PIN and PUK things on your SIM cards. Those are multi-symmetrical keys. Waseme mambo ingine, ...like mistallying or intimidation, hii ya GPRS is pure fiction.
In addition, besides an event record, voice is never recorded, except on voicemail.