Can i keep my iphone but switch it to straight talk with their sim card swap?

I know that straighttalk will let you keep your own phone and switch to straight talk. But is it possible to switch my iphone to straight talk?

If the iPhone is originally through AT&T, then yes, you can. All that requires is a sim card swap. Not to mention that Straight Talk is actually bounced off ATT towers.
If it's on another carrier, you'd have to unlock the phone, but that's kind of a gray area. Starting last Saturday, it's illegal to unlock your phone and switch it to another carrier.

Michael is correct. Hasto be an AT&T iPhone.