I don't know if the procedure has changed since I sold cell phones many years ago when they first came out (when the lightest portable phone weighed about 4 pounds!), but we were taught that when you use your cell phone, it pings to the closest cell tower. However, if there is a lot of cell phone usage, it will look for the next closest tower, then the next, until it finds a free one - which is why sometimes you get great reception, and sometimes it's horrible. Since we are talking about the day after Christmas, between holiday vacations and day after Christmas shopping sales, it's quite probable that cell phones that day were pinging far away from where they actually were.
Just my thought on the matter.