Since the launch of the iPhone brought a few million data-devouring 3G users onto AT&T’s towers, dealing with 3G in any major city was just a wee bit more efficient than sending a carrier pigeon. Well, things ought to be a whole lot better in San Francisco and New York now: like they’ve been doing in other places over the past few weeks, AT&T has fired up their 850 Mhz network in both major cities.

AT&T has long used their fairly hefty allotment of the 850 Mhz spectrum for aging TDMA technologies. By instead devoting this bit of radio to 3G communications, the network can handle significantly more users before grinding to a halt. As a little bonus, the 850 Mhz spectrum does a heckuva better job penetrating the concrete and iron bar walls of an SF or NY skyscraper – so expect general signal improvements indoors on top of the ability to actually, you know, use 3G.

Update: Maybe not? While AT&T says the upgrades are in place, comments are indicating that speeds in NY are as nasty as ever. Share your experiences in the comments.