One of the problems with AT&T Wireless if I recall are that they aren't a uniform carrier in that they aren't all GSM or all CDMA, etc. To me this is a drawback. When I was looking into buying a cellphone and checking out the carriers I wanted to go GSM but sadly, in the US, the GSM availability as well as the quality of the provider ended up driving me to go with CDMA and picking Verizon. My service has been excellent but I still think the GSM is so much nicer especially when swapping phones. A simple chip switch and yer good to go. Not so nice with non-GSM phones. Blah.
The good thing about Cingular grabbing AT&T is that it will provide a larger user base for GSM and hopefully, as a result, they will increase the size of the GSM network availability throughout the US. This is a very good thing for GSM. However, the real question is will they phase out the non-GSM offerings of AT&T or will they support it for existing customers and only offer GSM to newer ones? We'll see.
Hopefully sometime soon the Western Hemisphere and Europe will pull their heads out of their [censored] and come up with a world-wide GSM standard and not this 850/1900 Western Hemisphere GSM and 900/1800 European GSM.