What just happened? Apple says that "a very small percentage" of iPhone 12-series phones might suffer from a failure in a part of the receiver module, leading to affected units not being able to produce audio when placing or receiving calls. As a result, Apple has quietly launched a new repair program, intended to address this manufacturing flaw.
The "iPhone 12 and iPhone 12 Pro Service Program for No Sound Issues" offers a free repair to replace the defective module, where eligible customers can send their iPhone to an Apple center or Authorized Service Provider to carry out the repair.
Only phones manufactured between October 2020 and April 2021 are eligible, and -- as you'd expect from the title -- the 12 Mini and 12 Pro Max aren't covered (as they're presumably not affected by the issue).
Although a single component failure stopping such a basic feature from functioning is a pretty bad look, it seems to be rare enough that it hasn't seen substantial media attention before this announcement, and it's good to see any manufacturer getting on top of even relatively uncommon issues.
However, it's also worth noting that it's just a free repair for the receiver module; the company warns that units shouldn't be damaged in any other way when sent in -- and if they are, you might have to fork out to have the service center repair that damage. Apple also recommends that you should back your phones up to iCloud before shipping, as a just-in-case.
Assuming that your device meets the requirements, the program's coverage extends for two years after it was first sold at retail, and doesn't affect any existing warranty coverage on the phone.