Here is AT&T's new iPhone ad pointing CDMA only for Sprint and Verizon for the next iPhone. Why else to release the ad so late now with the new iPhone on the verizon. So, any chatter about LTE iPhone or LTE cell towers in Apple stores are nothing more than rumors.
What AT&T hopes to do is that as we approach the release of the new iPhone, it wants to remind everyone, including folks who currently are on AT&T but looking to jump ship, that the iPhone, current and the next one, is the only one that allows the user to surf and chat at the same time.
Personally, I've yet to encounter a situation where I've had to do both. Here is AT&T's ad.
Source: Edible Apple.