Unlocking iPhone 4s

Not at all compatable on ATT. Verizon is a CDMA network and ATT is a GSM network.

Actually, the 4S might have a chance of being used on a GSM network. From what I've heard, Apple is using a radio that does both GSM and CDMA (I'm assuming so they don't have to make multiple devices. From Googling, it looks like it's so you can use the phone in other countries too). If the phone was bought unlocked from Apple (at full retail) then it might work on AT&T (not entirely sure but it should if it has a SIM card slot). If it was bought on contract, have the current owner call Verizon and see if they'll unlock it.

lhamil64 is correct. Had to do a little googling. Hint, Hint  .  The verizon iphone 4s does support both GSM and CDMA and does have a micro sim slot but..... I have found mixed info.  Is the verizon 4s locked to verizon?  Will they sim unlock it? Will they discover a way to jailbreak it? What GSM bands does it support? Possibly no 3G?

So basically it may work in the near future but to what extent.  Also if you are able to use it with ATT then ATT will detect it and charge you a smartphone plan with data. Wouldn't it be better to just use an ATT 4s?

Some info for you here
http://www.macworld.com/article/162960/2011/10/how_international_is_the_iphone_4s_world_phone_.html