Following the Open Handset Alliance getting official, we noted the conspicuous of the US's two biggest wireless carriers, and dissected some of the reasons T-Mobile and Sprint were onboard but they weren't. According to the WSJ, Verizon's still mulling joining up, while AT&T "in part because it exclusively carries the iPhone in the U.S., is restricted from partnering with Google, people familiar with the matter say."
Another niggling issue for the juggernaut pair is Google's probable bid for wireless spectrum in the FCC's upcoming 700Mhz auction. If it winds up turning up its chunk into a mobile network, it'd be pulling a Microsoft by competing and partnering with them simultaneously, which apparently they don't take too kindly to.
Of course, this is on top of all the other reasons they weren't exactly clamoring to jump aboard in the first place. [WSJ]