On the Apple Online Store they have the unlocked iPhone 5c in two options T-Mobile Unlocked and Sim-Free. I'm assuming the sim-free one will work with local carriers when I am abroad. But for the iPhone 5s they have only one option, unlocked T-Mobile. It will ship with a T-Mobile sim card and there is no Sim-Free option. If I purchase the T-Mobile unlocked on September 20th will I be able to use it with local carriers abroad. I travel a lot therefore I need an iPhone that works with local carriers when I move from country to country. Any thoughts?