Can i flash a verizon iphone 4s to another carrier like metro pcs?

I've been searching for hours with no real solid answer… So here is a little background.
My sister lives out of town. She came to visit and told me how she bought a verizon iphone 4s that is a A1387 model. She bought it off craigslist and of course you guest it, it had a bad esn. I told her the first thing you should check before buying ANY PHONE is that the esn is clean… Anyway she ended up buying paying full price for a virgin mobile iphone and so i told her i would give her some money and buy the one she bought off craigslist and just use it as a ipod. I now wouldn't mind seeing if i have any options in using the phone.
So… What i'm wondering is
1. There's any way outside of a factory unlock I can unlock this phone. I no i can't jail break it it is running ios 6.1.3, but is there any way that i can unlock it for use with another carrier such as straight talk or pageplus
2.Is the Gpp unlock sim legitimate ( optional base on knowledge and experience)
3. Since the phone is cdma and gsm accessible, can i "flash" the phone to another service such as metro pcs. This option is the one i'm hoping for the most

Also any information on my options to get it working would be great. All answers and response I have found were mostly from 2012 and before the laws or whatever passed to forbid unlocking and etc after a certain date

In short, in breaking the law of contract with the carrier, you lose all your advantages and also you may have to pay some loses! Please contact your carrier to solve the problem maitain your rights by compromise?