This is a mobile phone sniffer circuit that can detect the signals being used in the GSM band at about 900 MHz. Since the signals are digitally encoded, it can detect only the signal activity, not the speech or the message contents. A headphone is used to hear the detected signals.
http://www.circuit-projects.com/rf-radio-frequency-circuits/cell-phone-detector.html
Information provided here may cause your phone to malfunction. Modifying the software of your GSM Phone is only a personal choice and shown for amateur purposes only. Commercial attempts based on these hardware and software may be possibly illegal. So take the risk yourself.
http://tacashi.tripod.com/gsmhack/gsmhack.htm
My goal is to build a kind of a mobile tracker. There are many different use cases you can think of but one of the obvious is a device, that is able to report where it is.
http://www.radiolocman.com/shem/schematics.html?di=52341
Discusses FDMA and TDMA too.
http://www.umtsworld.com/technology/cdmabasics.htm
Discusses FDMA and TDMA too.
http://www.tsp.ece.mcgill.ca/Telecom/Docs/cdma.html
http://www.davesgoldwing.com/cell_phone.html