AT&T is now reportedly suing Verizon over the ads, claiming that they mislead customers into believing AT&T doesn't offer any wireless service to large swaths of the country.
Although Verizon clearly labels the two maps it shows in the ads as representing 3G coverage, they've already attempted to mollify AT&T with a few changes including adding a "Voice and data services available outside of 3G areas" disclaimer in small print. This apparently hasn't been enough to satisfy AT&T, who continues to press on with the suit alleging the ads are confusing especially to non-technical consumers.
It sounds like the company is gunning for the ads to be pulled from the air. And to AT&T's credit, their 2G network does cover a much larger area of the country that isn't being represented on the map in the ad.