Could I unlock the At&t iphone 4 and put a verizon sim card in it?

The Sim fits I think I just need to unlock it.

Bob. Unfortunately you can't because they do not run on the same network. ATT runs on a GSM network and Verizon is different.

If you are trying to save money however I may be able to help you. I work for a company called Solavei. We offer unlimited voice, txt and 4g data for 49/mo. Your unlocked ATT phone would work perfectly with this service.

Go to my page at solavei.com/teamapex and sign my guest book in the top right corner.

No.

An unlocked AT&T iPhone will only work on other GSM networks.

Verizon uses CDMA and there's no way to make a GSM device work on CDMA networks.