My understanding is that only the GSM version of the 4s can be unlocked to work on any GSM network, but it won't work on CDMA networks....which would make me believe that you wouldn't be able to have your VZW CDMA 4s unlocked in the same manner (unlocked to use local sim cards when traveling abroad, but not to use on a different network in the US). I might be wrong but since Apple has a little note on their site when placing an order for the unlocked 4s states that the unlocked 4s can only be used on GSM networks and will not work on Sprint and VZW. So I would assume you could use that pne on T-Mobile and AT&T in the US....and any GSM provider abroad. There might be a way around that of course but it might not be an "official" or authorized method. Again, I may be wrong about this...
Verizon iPhone's can't be unlocked / hackivated because they don't use sim cards. Jailbreaking is fine but your stuck using verizon, but in my opinion...is the best anyway... if you had AT&T and unlocked your phone value almost could triple, provided the baseband can still be unlocked, for windows there is only like one program that does this (and don't pay on those scam sites, they take the free software and repackage it to sell, if even that most are just scams) for windows, sn0wbreeze will not update the baseband and mac i'd use pwnage tool both won't update and can unlock and jailbreak. But from what i hear most carriers still won't let you use unlocked phones and the main ones who will are AT&T and T-Mobile. If you Jailbreak you can change the carrier name to look like another if you want...I also have a fully connecting Siri on my iPhone 4 🙂
The 4S has and uses a simcard. They are locked to carrier. As long as you meet Verizon unlock policy they'll unlock the 4S. The 4 is a different story.
As mentioned, the VZW 4s DOES have a simcard which can be unlocked by the carrier if you meet the requirements (I believe it has to be on an active account, you have to be a customer for a certain timeframe...60 days Ithink, but I might be wrong on that). As far as the OPs question asking if an unlocked VZW iPhone will work (I assume they meant on another CDMA network in the US, but that's only an assumption) I would think that it could...if you got a simcard from another CDMA provider. Not 100% sure about that. As far as stolfi1's suggestion...aside from the fact that you aren't supposed to discuss that method on this forum it's not exactly an authorized method to do what the OP is asking. Yes, it's a method that exists but it's not one that is supported by any of the carriers or the manufacturer so it just depends on how willing someone is to go that route.