Would never work. AT&T uses GSM, the world standard in cellular technology, whereas USCC uses CDMA, an American standard, that's totally incompatible. They are compatible with Verizon on a couple of bandwiths, but overall not even compatible with them enough to consider a merger. The other big CDMA carrier, Sprint, runs only one bandwith, 1900 MHZ PCS so they're out of the running.

USCC's best option for a buyout is to invest in building out their LTE network at 700 MHZ where they will then be compatible with other CDMA LTE networks. Even then they wouldn't be attractive to Verizon as they have overlapping markets. But Sprint, which invested in WiMax and is behind every other carrier in the LTE race would be interested. It would be the easiest, and perhaps cheapest, way to get into the LTE race, not to mention upping their customer base.