I used to sell AT&T cell phones, and Spint as well.
98% of refurbs come about this way, a customer buys a phone. In a few days, for whatever reason (usually cannot afford the bill or want a different phone) return the phone. It is checked out by techs, diagnostics run on it. Repackaged and resold, but cannot be sold as new. So sold as a refurb unit. Much cheaper.
They still have the 1 year manufacturer's warranty from date of purchase.
Except for my first cell phone I have had nothing but refurbs. The one I had problems with was the brand new phone. 2 weeks, charger port goes out. Get a refurb unit, fine for 4 years. My last phone before upgrading to the skyrocket was a Palm Treo 750, had it almost 5 years, refurb. It still works great!
I'd say, save the cash and get a refurb if you can!