Not sure what all you have to do for different networks, You may need to take it to a store. You may have to do more than just stick in a Sim Card. You may have to change settings.
Looks to be in superb condition, barely used, if at all. May need to reset a factory reset before use. Box in ok condition but has stickers and may be messed up a bit. The box you receive may look worse than the one pictured. Here is what it said when checking the ESN.
Not Indicated This device does not appear to be globally blacklisted. Clear Device appears to be activation ready. The item "Samsung Galaxy S6 Box, Mint VERIZON UNLOCKED 32Gb Black AT&T Cricket SM-G920V" is in sale since Wednesday, December 30, 2015. This item is in the category "Cell Phones & Accessories\Cell Phones & Smartphones". The seller is "discountcdtoolsdvd" and is located in MIDWEST.This item can be shipped worldwide.