I live in Mexico, but I am from Virginia. I'm headed back in July, and I've already purchased an unlocked, contract free, sim-free iPhone 6 Plus from the Apple Store to use while I'm there and bring back here to use as my full time phone. When I activate it for the first time, if I use a T-Mobile sim to set the phone up, will it lock to T-Mobile? Will I be able to switch out that sim for my Mexican sim when I get back to Mexico? I'm just worried it will lock to T-Mobile if that's the first sim I use. My understanding is that with the unlocked sim-free phone purchased from Apple, I should be able to switch out sims as I please regardless of what sim I use to set it up. Is that right? I ask about T-Mobile specifically because so far, they have the best pay as you go International call plan sim that I've found for use in the States. It just makes the most sense to use that sim while I'm there. I normally just pick one up at Walmart when I get there.