I've been in Japan for a while and Ive only been able to use my phone over the UMA network, it works great but I dont know if its free? According to some websites its free to use your phone over a UMA network, as long as your not using the mobile network. But on t-mobile's website, it seems as if you have to have a plan? but if they cant tell where your calling from, how can they charge you a international rate? so confused and nothing has shown up on my bill?