I honestly did not know this was a thing until today. I'm not from the US.

Where I'm from, it is common to finance a phone as part of a mobile contract: your monthly payment includes a device payment and the network subscription cost. Typically 24 months, but in recent years I've seen 36 month contracts as well. But at the end of the term the device is yours outright. No further down payments needed. Usually the device payment is effectively 0% APR over the 2 years, so it's a pretty lucrative deal. I've purchased all my phones this way over the past 20 years.