AT&T iPhone unlocked for Verizon?

I have a Droid in Verizon. I don't like it too much because it's given me problems. My Mom has an upgrade for AT&T and she doesn't want to use it, so she might get me the iPhone. Could I unlock an AT&T iPhone 4S or 5 and use it on Verizon? If so, what would I have to do to unlock it and how could I connect it on Verizon's network? By the way, I have a 4G smartphone, so I have a 4G SIM card. Would the 4S or 5 still take the 4G SIM card if it's unlocked?

Yes, in THEORY

since the iPhone 4s is not an LTE phone, Verizon would have to be willing to flash it to their network, which they generally refuse to do.

Yes you can. You can call AT&T and request for a factory unlock. You'll need to give them your iPhone's IMEI number and they'll factory unlock your iPhone to use with other network.

It wouldn't work because the networks are different. Verizon uses CDMA and AT&T is a GSM network meaning they are incompatible. An unlocked iPhone only works on other GSM networks like T-Mobile.

A 4g SIM wouldn't work in a 4S because it's only a 3G phone. A 5 would need it cut down to a nano SIM and also need to be unlocked of course.

No it will not.AT&T iPhone 5 is a gsm only phone and Verizon uses CDMA. Same will go with the 4s. Even though its a world phone but for GSM only.

No it is not possbile cos they are with different carrier.

Yes you can unlock it. You should try this
http://jailbreak4iphone.com
This will help you to unlock any kind of iPhone.

Try to find solution here http://www.iphoneunlockfree.info