GSM/Worldphone
I too, have been curious about the GSM/CDMA WorldPhone feature. I've been doing a lot of research speaking directly to Apple and Sprint about this. This is what I found out. Basically, Apple and Sprint told me the same thing.
The iPhone 4S is a world phone that is GSM/CDMA compatible, as we all know it to be. It will be 'one' featured phone supplied to all carriers with no differentiation in specs., unlike the iPhone 4. I mentioned to both Apple and Sprint (obviously), I'd be going with Sprint on the 4S. Because I travel a lot for work (Sydney, Hong Kong, London, Japan etc.), and because Sprint utilizes CDMA only, I asked how I can access the world phone feature of the 4S when most of the countries I travel to is strictly GSM? I also mentioned I do not, and will not, roam due to the high roaming fees. According to an Apple Rep. and the Sprint International Department, the GSM Sim Slot will be unlocked, to allow anyone to insert a local sim card. In settings, it will allow you to "turn off CDMA", which allow only GSM to function. This is a feature not on the iPhone 4. By turning CDMA "off" in "network settings" and removing the Sprint Sim Card (supplied in the box) and reinserting the local sim card, this will therefore, prevent Sprint from roaming internationally. The iPhone 4S will detect the local sim card to allow anyone to use this phone freely. The downside, it your data functionality will not work, and you will need to access email via wi-fi. For me, I'd rather have utilization of the sim slot that to access data. So this works....
(F.Y.I. The International Text Messaging Plan for $10.00 will only work when your in the USA texting out. When you travel abroad, text fees applies. .50 cents to send and .20 cents to receive.)
The claim is, Sprint has your money by signing a 2-yr. contract, so they don't really care, what you do with your minutes, whether you use them or not. Most people do not travel out of the country anyway. And those that will, will benefit from this feature.
Lastly, with non-smartphones, there's already a feature to prevent the phone from roaming to allow it to strictly use Sprints network to prevent high roaming fees. Basically, the same feature will be on the 4S, but will apply internationally, since domestic roaming is all covered locally by Sprint.
I hope this helps, and I hope what I've been told is indeed fact.