I assume you have the service with AT&T then...
My family is with T-Mobile and when my sister was looking for one, we bought it outright (unlocked) because it would be cheaper. The main reason why is that the edge, jump, and next plans from Verizon, T-mobile, and AT&T respectively, will stick with you even throughout the phones life, and that there are no "free" upgrades included with the plan, even though that's what they attempt to sell.
I always ask people when they say they got a "free" upgrade, and ask them if their bill went up (or if they even look at it) and always, always, always, it's a yes..
But anyways, with T-Mobile it would've been $26 for 24 months, and the additional 10 per month on the bill, say for the life of the phone. So essentially $240 more added on to the phone...