This is a bigger anti-trust issue than you'd think; the Bush administration didn't let the VZW-Alltel deal go through without making Verizon divest certain parts of the network that overlapped. Most of those went to AT&T. THe remainder...where both Verizon and AT&T had significant service on their own...went to ATN (new Alltel).There's a reason AT&T didn't get the spectrum and customers the first time.
Then again, ATN probably wants out at this point (it's tough being a spread-out small wireless carrier, competing against companies 100x your size), and maybe AT&T is really looking for ex-Commnet spectrum, which was never part of the old Alltel and thus isn't as big of a competitive issue.
But I don't trust the "not as much of a competitive issue" side when we're talking about a company that tried to become the only nationwide GSM provider in the US by purchasing a company whose footprint almost completely overlaps with AT&T's.