Is iPhone 4s compatible with all carriers?

[NYRangers11]

I am trying to sell my iPhone 4s (Verizon) just like most people who are due for an upgrade. I am just not sure how to market it. The phone was unlocked by Verizon to work internationally in other countries. I am just not sure if it will work with ATT or Sprint. Can someone help. Is there something I can do to unlock it with USA carriers such as ATT or Sprint?

Also the phone has been reset since the international unlock, wondering if that reset the unlock as well?

Thanks in advance for all the help

 

[Intell]

It will work on all carriers except for US GSM carriers and possibly Sprint and some other CDMA networks.