Best Place to Buy a Phone that Isn't from the ATT Store?

So I plan on purchasing a new phone either today or tomorrow.

Currently looking at the Motorola Atrix. I'm not eligible for a renewal and ATT charges 450 dollars for the phone without a contract.

I've seen the phone on craigslist averaging from 280-330 brand new.
I'm a bit skeptical buying a phone off Craigslist, but am not opposed if I find a legitimate seller.


What im curious about is if anyone knows stores that sell smartphones in Houston for decent prices.

I don't want to get shanked by ATT and pay 450 but I dont want to get a busted phone for 300 either.

Advice would be appreciated