If I buy an unlocked ATT iPhone 4S can I use it for boost?

There's an iPhone 4S on eBay that's been unlocked, so I was wondering if now that Boost Mobile sells the iPhone if I would be able to switch the old ATT phone to boost mobile?

AT&T is GSM (uses SIM) and Boost is CDMA (doesn't use a SIM) so they're incompatible. Don't buy it if you want use the phone on Boost.