I've been lurking for awhile and thought i could shed some light to this. I have a buddy who works on the servers for sprint here in KC. He said that there has been an Iphone accessing the sprint servers occasionally over the last month or two, so that means there is a CDMA Iphone in existance. Now that doesn't mean its a Sprint Iphone, it could be a verizon one because they pop up on the system if they are roaming on a sprint tower. He is digging around to find out more, but from what he has told me, he hasn't been able to get more info. Take that for what its worth.
I trust him, he has tipped me off to a few phones that i hadn't heard of before they were announced, like New blackberry coming out at the end of the month and the Moment 2 that is being tested right now.