Buying a phone over Ebay

So here's my story-

My past three phones have been sliders, and all three have broken down. The first two the buttons stopped working, and now my newest one's screen keeps going white and I have to wait for it to go black again and refresh it so I can go on with my business. So I've concluded sliders can go screw themselves, and I want to move on to a Blackberry. I went to my local T-Mobile store (I know I can send in my phone to get the same type back for free, but I want to rid myself of sliders), and asked if I could buy a new phone. They said I have to have my current phone type for 22 months or something along those lines, so my only choice was to send it in to get a free one back. What the ****?

I really don't get that policy, as buying a phone is just buying the hardware, (So now I conclude T-Mobile can go screw themselves) so I decided I wanna buy a phone off Ebay. So my question is, if I bought one would I just be able to pop in my SIM card, and it would work just fine? Of course I would check and make sure I'm buying from a good user with good info. Thanks for any help :)

I bought a storm of of craigslist and it works fine. It was a verizon phone already so i had no probs. The treo i had bought from ebay was junk, just watch out where you buy one from. So i know as long as it is from the same carrier it should work, or prob even being an unlcoked one. But i am not 100% sure on the unlocked one. Maybe this helps a little.

Yeah, that helps. I'm finding a few good looking ones off ebay, they're "top-rated sellers" and they're all unlocked phones. Thanks :)

I love the storm I have. It is prob the best phone I have ever owned to be honest. Does so much and has alot of helpful apps. Crackberry.com has alot of info on blackberries, apps, etc.

Anyone know why this isn't getting any bids? It seems like a good deal to me:

http://cgi.ebay.com/Blackberry-Curve-8900-WiFi-GPS-PDA-Cell-phone-T-Mobile_W0QQitemZ180451644487QQcmdZViewItemQQptZPDA_s_Pocket_PC_s?hash=item2a03c19447#ht_3913wt_732