Such a goal is beyond your capabilities and you should abandon the idea. Mobile phone signal decoding is an extremely complex task. All decoding done in mobile phones is done within highly integrated chip sets that incorporate powerful DSP functions in addition to general purpose controllers and the decoding part of this type of chipset alone represents many hundreds of man-years of software engineering. You cannot have access to the interfaces to these chips without considerable cost, difficulty, risk or luck. If you must study the idea further, focus on GSM technology. The essence of the signalling protocols are defined in 3GPP specifications which fill many books with arcane engineering detail. You can find the specifications by going here: 3GPP - Specifications
i dont know a whole lot, but a cell phone is nothing more or less than a hand held radio the sim card contains info . thats y you can take sim card out and put in another phone and it has your number... vervison is the only people that dont use sim card the phone containts the info
ou are correct Fireman, you dont know a lot. Re-read RadioRons response. No radio communication in todays age is going to be simply a matter of receiving, and transmitting signals back and forth with no protection...dont be so silly