What alltel phones are compatible with a verizon contract?

I'm looking into buying a used cell phone and I wanted to know if there was anywhere I could find a list or something of phones that are compatible with a verizon contract that aren't verizon phones because I've been reading up on it and Im getting mixed answers about whether or not you can do this for sure or not so I would really appreciate someone who maybe works for verizon or something I just want a list of compatible phones or maybe a type of something I should look for on the phone..? I apologize that it sounds almost vague but I really don't know much about any of this..
Thanks!