So here's the latest "world phone" info from everything I've been able to source, including official statements from Sprint and Verizon.

Sprint have debunked a rumor stating their phones would have an unlocked GSM SIM slot. Their phones will come with a SIM and the phone will be locked to that SIM. A so-called "roaming SIM" that will be used when you're traveling, the same way an ATT SIM would be used.

Sprint will not be unlocking phones and further claim that the SIM is non-removable. I doubt this last part, but have no reason to doubt that the phone is fully locked down. Quite possibly forever.

Verizon claim that they will "international unlock" any phone, including the iPhone, after 60 days have passed of "good standing" on your account. There is no way this unlocked state will work with other carriers in the US. Their phones may also be forever locked out of using other US carriers.

Buying a Sprint or Verizon phone gives you the possibility that one day it *may* be unlocked for GSM/UTMS , but it will always be locked to the original CDMA provider. There has been no news to indicate you will ever be able to move a specific phone between Sprint and Verizon's CDMA networks.

Clearly, buying an UNLOCKED iPhone 4S from Apple is not the same thing as buying a Sprint or Verizon phone, whether they unlock at a future date or not. The factory-unlocked phones do not have any CDMA capabilities. You will never be able to use them on Sprint, Verizon or any other CDMA carrier in the world. They are strictly GSM/UTMS phones, the same as iPhone 4. The Sprint/Verizon phones may never be able to use other US-based networks at all. As far as I know, there is no mandate to force carriers to provide unlocking capability/service.

EDITED: Sprint re-states SIM slot usability. John Gruber posts image of Sprint phone with ejected SIM:

http://daringfireball.net/misc/2011/10/sprint-sim.jpg