Dealing with sockets is typically OS-dependent. What OS are you working on? If Un*x, I suggest purchasing a copy of "UNIX Network Programming" by Richard Stevens (ISBN 0-13-949876-1).
Alternatively there are platform independent libraries available that encapsulate the kernel socket interface for you. The Boost asio library comes to mind as one.
If this is a professional endeavor, you've jumped-in over your head. You need to do a lot of learning about mobile communications protocols. Whomever your employer is should be able to provide you with specifications of the hardware you will be working with.
If all you have to do is make the mobile unit itself interact with the existing infrastructure, then your employer should provide you with exact specifications on how to negotiate with each broadcast tower.