Visiting Atlanta multiple times recently, I have had great success with Tuner2 Internet radio on iPhone each time. Most recently, my rental was some kind of "crossover" vehicle from Chrysler with absolutely no headroom. However, it did have the requisite AUX jack, so I plugged in and listened contentedly getting to my meetings around the city. I guess I shouldn't be surprised, though, AT&T makes its home in Atlanta, so I would hope that in their home city, they would be solid. (Of course, we have seen home town apathy before...)
Side note, during a brief sojourn onto the FM dial, I heard a commercial from Comcast. In Atlanta, are offering their High-Speed 2go (awkward spelling) bundling 4G, 3G, and home cable into a single bill. $50/month for the cable + 4G, $70/month for cable + 4G + 3G for roaming. Pretty good pricing. Of course, it is only available in a couple cities so far.