They monitor traffic, I assume. I have historically used both PDAnet and FoxFi among others...all get shut down within a few minutes, and I receive a text telling me to sign up for tethering service. I'll try it again after rooting the phone, to rule out simply detecting all the common tethering apps, but I'm guessing they're detecting NATted traffic or similar.
I'm considering picking up a Nexus 4, rather than bothering with rooting and re-imaging the Sensation. I don't really like the Sensation, though all the problems I have with it could be due to software. It's a custom build with Sense, which I really don't like.
Anyway, it's a new phenomenon. I was tethering on T-Mobile for years without trouble. About two months ago, they started shutting it down after a few minutes of use, and redirecting all traffic to their T-Mobile site upgrade page.
I'm considering picking up a Nexus 4, rather than bothering with rooting and re-imaging the Sensation. I don't really like the Sensation, though all the problems I have with it could be due to software. It's a custom build with Sense, which I really don't like.
Anyway, it's a new phenomenon. I was tethering on T-Mobile for years without trouble. About two months ago, they started shutting it down after a few minutes of use, and redirecting all traffic to their T-Mobile site upgrade page.