I originally wrote this entry on September 22, 2004, and published it on blogs.sun.com.
Global System for Mobile Communications (GSM) is the grandfather of most 3G mobile network environments.
GSM's success was not so much dependent on the architectural definnitions that it put together for public land mobile networks (PLMNs). The main reason for its success has been the standard interfaces it defined which made roaming across operators easy. For a description of the interfaces, architecture and system design, I highly recommend Gunnar Heine's excellent book GSM Networks: Protocols, Terminology, and Implementation. This highly readable book (how often can you say that about a telecommunications protocols book?) was originally written in German: GSM--Signalisierung verstehen und praktisch anwenden.
Not only easier roaming was achieved by GSM . . . It also made mergers (such as the recent one between AT&T Wireless and Cingular) easier.
This morning, it looks like Cingular has finally integrated the AT&T Wireless home registries. My carrier was AT&T Wireless. I had spotty reception in certain locations which apparently were owned by Cingular but were not being shared generously before the merger. After the merger, I first noticed an improvement in signals on my phone due to better cell coverage, but a number of new problems with direct dialing of my own landline number when mobile in my own area code. When in the newly available Cingular cells, I had to dial full long-distance number of my home. This had something to do with the slow integration of home and visitor registries. Now, that the integration seems complete, this new problem has also disappread.
More cells, better reception . . . make me a happier user.