Most cell towers are not omni-directional, they are segmented. It's quite common to have 3 or 6 separate segments on a cell.

It's possible to get quite an accurate arc depending on local configuration, from just a single segment. It improves significantly with two adjacent cells and dependent on the local configuration of the segments you could get a single location (dependent on whether the segment arcs intersect once or twice). The more segments per tower, the greater your chance you can pinpoint with just two towers.

By GSM, I also include UMTS.

From personal experience, I've seen none of these problems in the UK. Granted, our peak population density is about half that of big cities in the US (New York vs. London), but our national population density is an order of magnitude greater (1000 sq/mi (england) vs around 80 (USA) - or 650 sq/mi (UK) vs 80 (US)).

Seems to me that AT&T's network is just a bit crap. We have a bit more experience of running GSM networks over here!

Having said all that, O2 have had some spectacular cock ups on their data network recently, although not related to coverage/dropped calls.

So this thing is so advanced that it can time travel into the past and delay its own repairs?