I see a lot of listings on eBay for "factory unlocked" S4's and generally they claim they work on carries with a correct SIM card for that network. My understanding though is they may "work", but may not support all bands / frequencies. Meaning technically it will "work", but may not work on 4G, or work for voice, etc. So is there such a device that is Unlocked that will work completely on Verizon that isn't made for Verizon's network? Thanks.