Can an iphone 4s (GSM) be activated on a CDMA carrier?

I wan to buy an iphone 4s but the one that I found cheaper is from AT&T (GSM) and I wanted to know if I can unlock it to an international CDMA carrier.

Yes it's a world phone, however you need to get t unlocked first

No, GSM iPhones only work on GSM carriers, and CDMA iPhones only work on CDMA carriers.

This is also true for other phones besides iPhones.

So the only international carriers a GSM iPhone can work with also have to be GSM.

The situation is a little different for CDMA iPhones; I'm pretty sure the most recent ones from Verizon are capable of working on GSM when they're overseas (Verizon also has several Android phones that do this).

Also, GSM in the USA uses different frequencies from GSM in other parts of the world, and the same goes for CDMA. Most (but not all) GSM phones are multi-mode so they can handle GSM anywhere in the world, but I don't think that's true for CDMA - in fact I've never heard of a CDMA phone that could work on anything but the carrier it was made for. For instance, even though both Verizon and Sprint use CDMA in the USA, and even though I've seen questions for several years here about activating a Verizon phone on Sprint or vice-versa, I've never seen any evidence that it's possible to do it.

No you can't.