Can I switch a AT&T iPhone to Verizon?

I currently have a Verizon iPhone 4, a friend of mine has a AT&T iPhone 5 that they want to give away. I want to know its it's possible to switch a AT&T iphone to Verizon?

No.

AT&T can only switch to other GSM networks (like T-Mobile)

Verizon uses CDMA, and as such, isn't compatible with AT&T phones.

You would have to get a 4G SIM from Verizon and put it into the iPhone 5 and see what happens. My guess is that calling and texting would work but data probably wouldn't.

P.S.Re. That other answer about CDMA vs. GSM, that was true for older 3G phones, but with 4G/LTE even Verizon phones use SIM cards.

Iphone 5 is both gsm and cdma, anything before that then no since they are specific types.