I have a Verizon iPhone 6. As I have seen T-Mobile's service expanding in my area, I kind of would like to test out how things are. It looks bad to be honest, but I just want to know how bad. I was thinking, I could just get a pre-paid T-Mobile SIM, and it would work in my Verizon iPhone 6 as it has CDMA and GSM bands, and the same iPhone model is sent to Verizon, AT&T, and T-Mobile customers. However, I'm still under contract. What kinds of horrible things would happen if I put a T-Mobile pre-paid SIM in my iPhone? Would it just not work? Would it throw a huge charge on my phone bill? Just curious. I can't really partake in T-Mobile's "Test Drive" program as their nearest store is 100 miles away, and I think I read into it and you have to return the phone to a store.