Att IPhone 4s change to Verizon?

I want to give my iPhone 4s to my mom, but I have att and she has Verizon. Does anyone know if this is possible and how to do it?

Call att and ask them to unlock your phone. They will probly say no so then you go to a phone shop not service shop and have them unlock the phone from the service for$20. Then go to a verizon shop get the service. Then your phone goes crazy for 24 hours. Then it is on verizon servicr.