There was once a time when you had to fish out someone that would unshackle a smartphone from the clutches of a specific carrier, but those days have come and gone. Apple doesn't want you to weed anyone out, trade SIM cards or rush into any specific carrier's contract just to own an iPhone.
Apple has started selling SIM-free versions of the iPhone 6 and 6 Plus – there's no more two-year contract or purchasing an unlocked model through T-Mobile.
If you're wondering why the SIM-free version of the iPhone is necessary or even needed consider the binding woes of a two-year contract or perhaps even traveling abroad. If you carry an unlocked iPhone when going abroad you could use a local carrier in the area and avoid roaming fees. The SIM-free versions of the iPhone start at $649 and can end up around $949, depending on the amount of Gigabytes you as for.
Once you get the SIM-free version its as easy as starting up with a carrier and inserting the SIM card.
[Apple]
