Looks like AT&T is out to give customers a headache. In an analyst meeting AT&T expressed interest in becoming a mobile virtual network operator (MVNO) once they receive the AT&T Wireless brand name back from AT&T Wireless (which they lose upon merging with Cingular, as the AT&T Wireless name is under lease).
If AT&T were to become an MVNO, they would then partner with another major network and become a brand name to sell product. But this means nothing but trouble for the current AT&T Wireless customer, as their phones will be part of Cingular, while a new AT&T brand name arises (possible under a completely incompatible network). If you’re confused already, it can only get worse from here.