To see if you are eligible to make the switch to AT&T Next, dial *NEW# and you can start the ball rolling. Once you join AT&T Next, you put nothing down and pay off your new phone over 24 months. Once 12 months has gone by, and you've paid off at least half the balance of what you owe on your handset, you can trade it in for the latest and greatest model, and start the clock all over again.
If you're an AT&T customer always looking over your shoulder to see what phones your friends, family, and even random strangers on the street are using, and you always feel that pang of jealousy, you might want to consider AT&T Next.
source: AT&T via Engadget