I have an S 5 on Verizon but will be traveling and want to know what networks I can use. I want to use prepaid for places I wont have WiFi coverage for their "unlimited" data. I have found some GSM based carriers like T Mobile and Straight Talk but I am unsure if my phone will work. Also, what service should I use to unlock my phone? I found a shady one that's free but I am not too comfortable about that.