Fortune reports that AT&T is about 73 percent finished with its major metropolitan area 3G network rollout. That means that it currently has 275 markets blanketed with their new high-speed, cellular data network, with a total of 350 expected by the end of 2008.

"Don't be confused, be reassured," the report said. "If you buy a hot new 3G phone from AT&T, it will certainly zip along at top network speeds as long as you aren't trying to use it in those markets where it isn't yet available."

In other words, today's AT&T cell phones that are 3G compatible (except for a certain well-known model, which isn't) will automatically find and connect to the faster networks whenever they're available, once the carrier flicks them on in their respective cities.

However, and this is important, the reverse is not true: if you buy a phone that's not 3G compatible today, it will never work on those high-speed networks, since the data radio inside can't be upgraded. (It's a hardware thing, not a software thing.)