By Laura Northrup
Tethering is using your smartphone as a mobile wi-fi hotspot. It's a handy way to get online when you're, say, stuck at the dentist's office and need to turn in some work. It's also against the rules for customers with legacy unlimited-data plans from AT&T, for obvious reasons. One customer who has one of these plans is currently fighting with AT&T: they want him to stop tethering, and he says that he isn't.
Ars Technica took on this question about the fundamental nature of reality and of phone plans, trying to figure out between AT&T and the customer what was happening here. AT&T told Ars that their customer, Evan, "is using an unreleased mobile OS downloaded from the Internet."