content: Tethering is essentially like doing all of your activity on your phone (browsing, downloading files, chat, voip calls, etc), but then immediately copying that information over to a computer via USB, wifi, bluetooth, etc. Differentiating tethering from regular phone use is just bullshit marketing from corporations trying to suck as much money as they can from you. Data doesn't even COST them anything.  Not on its own at least.  ISPs charge each other for peering fees.  Those fees are determined by the 95th percentile of traffic. Let's say T-Mobile had an arrangement with a peer (the ISP they connect to in order for their subscribers traffic to reach the rest of the internet) at 95th percentile of 100mbps (yes, unrealistically low, this is just an example).  Traffic could flow at 95mbps and they would never hit an overage.  As long as their customers pay their bills, there's no problem.  If total traffic was at 5mbps, they'd make a pretty good profit.  Obviously they want that case. So how do they address the problem?  Well, they just keep that link running at 95mbps.  Subscribers would be locked into a certain transfer rate (95mbps / total number of active subscribers). Problem solved, no overages, T-Mobile makes money, subscribers never hit a data cap.  Every  5fa0  one is happy. But companies are greedy.  They want to screw you over as hard as they can.  So what do they do? Like I said, ISPs like T-Mobile, and the companies they peer to, negotiate prices based on link speeds (Mbps). But T-Mobile and other customer-facing ISPs (AT&T, Comcast, &c) charge customers by amount of data. If they charged each customer based off link speed, all of this shit would go away. What's even worse is that with peering agreements, if company A sends 100mbps of traffice to company B and company B sends the same RATE of traffic back, then they don't charge each other anything.