Update...

I was on the Metro today and decided to see how the iPhone held up. I'm a little surprised... WMATA/AT&T didn't manage the screw this up. I got on at Vienna and, of course, had signal until Ballston. Ballston to Rosslyn had no service. But for the rest of my journey, I was able to get service on the platform/while waiting for the train to depart. Some of the stations are close enough where you can manage to keep your signal while the train is in motion. My iPhone showed me having all my bars and 3G.