GSM is a globally accepted standard for digital cellular communications.
GSM uses narrowband Time Division Multiple Access (TDMA) for voice and Short Messaging Service (SMS).
This tutorial helps you to understand GSM Basics and should be your starting point.
This reference has been prepared for the beginners to help them understand the basic to advanced concepts related to GSM.
Before you start doing practice with various types of examples given in this reference, I'm making an assumption that you are already aware about some terms related to Telecom.
(1) GSM Quick Guide
A quick reference guide for GSM.
(2) GSM Useful Resources
A collection of GSM Sites, Books and Articles is given at this page.
(3) GSM Tutorial in PDF
Download a quick GSM tutorial in PDF format.