If you buy full price device only from the Apple retail store any version you buy will be unlocked.
The unlocked version from the Apple website is the T-Mobile version. The other versions sold through the Apple website require you to enter a phone number and will be locked to the carrier. If it is locked to the carrier and you paid full price you have to call the carrier and request an unlock. They will grant the unlocked since it was paid full price and you're not bond by a contract with them.
It's less hassle just to buy it device only full price from an Apple retail store if you want an unlocked version.