Sprint iPhone 4 migrate to Verizon?

I have a Sprint iPhone 4 that has been deactivated from my Sprint account and wiped/restored. Initially, I did that because it was damaged, however it is still functional and I would like to send it to my Mom so she can have her first smartphone. Where she lives, the only service provider she can get is Verizon. Will my old Sprint (no SIM card) iPhone 4 work with Verizon? I've heard that Sprint phones are sometimes hard to switch around.

The Sprint phone would need to be "flashed" to work on the Verizon network.

You heard right. Why? Sprint's policy (until the law goes in effect Feb 2015) is to never unlock their phones for use on a rival carrier. You have to purchase an unlock code online and 'free' it up for another carrier's programming. My cents worth, sell or swap someone for a Verizon 4 to make it easier. Best luck.