[ReignOfError]

The new phone is unlocked. That’s how it comes from Apple when you walk into the Apple Store and pay for it. You are getting a locked phone because you are buying through AT&T.

You have no idea what you're talking about. The Apple store sells phones locked to the Big 4 carriers, in addition to unlocked phones.

[dinodino]

Just heard back from my friend. The phones he took back to Saudi were purchased at an Apple Store in Orange County, California. In his words, “I got a couple iPhone 6s & 6 plus. The T - Mobile version is unlocked, meaning you can use any GSM Carrier SIM Card.”

So, there you go. The phones were unlocked right out of the box.