How to convert a verizon Iphone 4 to at&t and add a new number to it?

My iphone broke and it was on at&t but my friend had a extra iphone 4 that is on verizon. It is jailbroken btw. So my question is how so i unlock a verizon iphone 4 and how do i transfer my at&t number to it?

I do not believe that the Verizon iphone (CDMA network) can be used for AT&T (GSM network).

What are all the differences between the iPhone 4 (AT&T/GSM) and the iPhone 4 (Verizon/Sprint/CDMA)?

http://www.everymac.com/systems/apple/iphone/iphone-faq/differences-between-att-gsm-iphone-4-verizon-cdma-iphone-4.html

You can't unlock verizon iphone 4. Yes, unlocking would allow a phone to accept any simcard, you can put your att simcard into an unlocked phone. But there no way to "unlock" this phone as it has no simcard slot.