AT&T Wireless time service
I have cell service with AT&T wireless. One feature of the service is network time updates. It fortunately includes a confirmation. It’s great when you land in a new city. It hasn’t been so great last night or today. Last night, at 23.20, I got an update telling me that the new time was 21.15. Just now, I got one telling me that it’s 10.15 (It’s actually 10.30.)
There are a whole bunch of security protocols which rely on having roughly correct time. I hope none of them are implemented with a reliance on the PCS network.