Extremely common for carrier provided phones. Especially the highly subsidized prepaid ones.

Verizon already has this 60 day policy, including for its wholly owned subsidiary MVNOs. T-Mobile is six months. A lot of other prepaid MVNOs are one year.

If you are buying from Apple, it's generally unlocked. I'm not aware of Apple directly selling locked iPhones at all anymore.

They still exist, but I think these days there's a bit of confounding with carrier-subsidized phones. The phone isn't technically locked, but if you switch carriers before the subsidy has been paid off, you owe the remainder of the phone's price -- usually it's rolled into some kind of Early Termination Fee.

There's also some amount of regional locking, some phones might not be licensed to operate in the US but are in Europe, or vice-versa.

Not only its carrier-locked, it is sometimes model (variant model) specific so after unlock you are still stuck with that carrier because the other carrier will not take it.

For instance, after 1 year T-Mobile paid service it finally unlock your phone, thinking about moving to AT&T. AT&T and its MVNO Cricket Wireless actively disconnect your service when you put the SIM card to an "unsupported phone" just because it is not on their list.

In my experience I've never had trouble unlocking a paid off phone. Sample size of three carriers.