>Cellular phones such as iPhones cost hundreds of dollars. To make the phones more affordable, during the relevant time, AT&T subsidized the purchase cost of phones or sold phones to customers under installment plans. Unlocking a phone effectively removes it from AT&T’s network, thereby allowing the account holder to avoid having to pay AT&T for service or to make any payments for purchase of the phone.[0]

That's the argument from the DOJ. ~1.9M phones were unlocked and losses were estimated at $200M in unpaid fees. Back of the napkin math, but that would mean around 15-20% of users had balances owed on the phone. The rest were people just trying to make the thing functional.

I've been looking at the Surface Duo because I really need a pocket-sized tablet more than I do a cell phone. It recently went on sale, but locked to ATT's network. Legally, they are obliged to unlock the device on request. They can charge a fee if the hardware was intially subsidized, but they must unlock it. I was more than ready to pay full price for the phone until I saw what it would take to legally unlock the phone. Call agents didn't understand the process, there was conflict on whether ATT or Microsoft would have the ability or obligation to unlock. It would require multiple tickets and weeks worth of waiting, and you may end up with an unusable phone. If I hadn't done my research and was left with an non-functional device I definitely would have looked for alternative methods.

[0]https://www.justice.gov/opa/pr/fraudster-sentenced-prison-lo...