AT&T and T-Mobile: Good for whom? | Dialed In - CNET Blogs
Another good read...
I agree AT&T's customer service sucks, it's a known fact why they have been in last place for the most part over the years. It's also the fact, if it works, you don't deal with customer service (I never call Verizon unless I have a problem or need a new phone, AKA problem).
I only see it as a coverage thing, Between AT&T and T-mobile, the GSM coverage in the US will be great once they are combined. That is what I see here.
As it stands, GSM is questionable in a lot of areas, it could get a lot better.