Cell Phone Technology
A note about monitoring Cell Phones: It is illegal, do not do it. It does not fit under the same rules and regulations that pertain to the rest of the radio spectrum. The U.S. Congress passed rules which they thought would further protect the privacy of individuals (which were led to believe they had privacy on wireless systems equal to the privacy on wired systems).
A good general overview: http://www.howstuffworks.com/cell-phone1.htm
Detailed Explanation: http://www.ericsson.com/support/telecom/part-d/d-2-4.shtml
Analog Systems band plan: