I own an unlocked iPhone 6s I purchased from AT&T that has been unlocked by AT&T. I've been looking at switching carriers to either Verizon or T-Mobile which seem to offer better calling packages. Verizon has confirmed that the iPhone 6s's IMEI number works on their network. What I don't know is how well this works and wondered if anyone had any feedback if they've done this before. I would prefer not to have to sign-up and then find out it works but not very well. T-Mobile from what I understand should work and they are offering a very good calling plan, at least for me, since I call Canada and México frequently. I don't know how well this works either since I believe AT&T's iPhone 6s does not have T-Mobiles extended frequency/network as if the phone was purchased from Apple or T-Mobile directly. If anyone can help offer any suggestions, advise or their own experiences I'd be grateful. I really don't want to have to keep paying for "start-up" fees to be able to test and see which carrier works best with this phone. The data usage and speeds are not that much of an interest to me, I currently use less than 200mb per month now.