Can I change a Verizon iPhone to a ATT iPhone?

Okay so here's what's going on, I have an ATT iphone 3 and my best friend had an iPhone 4 but she was with Verizon. She was du for an upgrade and ended up getting an Galaxy phone and gave me her iPhone 4. Problem is, it's verizon and I'm ATT
Any ideas as to fix that so I could have it as my phone?

I'm not sure how ATT's service is, but I've had Verizon for 7 yrs and I love it. I'd never switch!

I think the Verizon iPhone 4 won't run on AT&Ts network

Nope. There's no way to do that. CDMA phones can't work on GSM network.