BIG caveat:
Per
Compare iPhones:
AKA, if you have any desire at all to work on a CDMA network, you
must buy an
activated iPhone 4S on a CDMA carrier (Verizon or Sprint in the US.)
It appears that the CDMA-active iPhone 4S will be unlocked world-mode on the GSM side, but you must go on a contract.
Also in the footnotes:
So it appears there will be no unlocked CDMA phone. I would guess (although we won't know for certain until 10/7, the day you can order,) that this means that you will not be able to buy non-contract CDMA phones, either. Right now, the only non-contract iPhones you can buy are the non-S iPhone 4, GSM-only model at $549, or the 3GS 8 GB at $375. (So either you're getting gypped on the subsidy on the 3GS, or a deal on the 4 - the with-contract price difference is $99; the non-contract price difference is $174.)
I was planning on switching to Sprint, but was hoping to get an unlocked, non-contract phone so that I could switch to Verizon, AT&T, or T-Mobile without waiting two years...