Per a report by 9to5Mac pointing to an Apple support thread, newer iPhone users on the latest version of Apple's iOS operating system, including 15.1.1, are running into dropped calls. Phone calls tend to drop out between 2 to 8 minutes after they start.
"I have the same problem with dropping calls. I have a 2017 Tundra and an iPhone 12 with 15.1.1," user Tundra_2017 posted in Apple's forum. "The only workaround that I’ve found is to connect the USB cable from my truck to the phone."
The problem seems to be limited to cars not running Apple Car Play, instead using the car's on-board infotainment systems. For some users, this problem was not occurring on iPhone X units.
"Spent an hour on the phone with Apple today. Uploaded diagnostics from my phone. They told me to call Verizon, it was a network issue. Huh?" user Jon55nj posted. "Bluetooth has nothing to do with Verizon. Should have returned this immediately when the problem started but I thought there is no way this wouldn’t be sorted out soon. Wish I had my X back."
At the moment, the simplest solution seems to be to use a USB cable and forego Bluetooth altogether.
As of this writing, an Apple representative has not replied to the thread. Users have not been able to figure out a solution either, other than to use a USB cable for the time being.
An issue similar to this did not pop up in our iOS 15 review. But as with any new operating system update, there are only so many permutations testers at Apple can go through. Really, it's when the operating system is out in the real world do many of these more minor bugs get squashed. Until then, users might have to wait for the next incremental iOS update for a permanent fix.