[Q] HELP! Can I switch the AT&T S3 to Verizon?

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http://forum.xda-developers.com – I have Verizon, a Motorola Razr (Not MAXX) and it is crapping out on me, running slow, not sending picture messages etc. My boyfriend has a trading post type store and he bought a brand new Galaxy S3 but it's through AT&T. When I put my SIM card in the S3 it asked for a SIM Pin for unlocking. I have experience rooting a Nook Tablet so with some directions I'll probably be able to do it, I just don't know where to even start. Do I just unlock the phone or is there a way to switch it over? Thanks!! Ashley (HowTos)