When I upgraded to 4.0 from the backup iTunes made, it kept the profile I got from benm.at that I was using in 3.1.2. When I upgraded, tethering was kind of working - the computer could connect to the internet through USB or Bluetooth, but I had to force restart the iPhone when I was done using it because the screen would just stop responding. I'm on T-Mobile US's $10/mo data plan. EDGE is okay for me. I thought I would try reinstalling the profile so I uninstalled it and went back to benm.at, but for some reason Safari told me "Could not install profile because of an unknown error." So I instead went to iphone-notes.de and had a tethering profile emailed. I installed it and cellular data works on the phone but the internet tethering option didn't appear in settings. I opened SBSettings and clicked the red tethering toggle...it turned green! I went back to settings and the tethering option had appeared. I connected the phone to the computer and the tethering option didn't disappear, but the computer wouldn't connect. It said "network cable unplugged." I checked the phone - the tethering option was set to on, but there was no blue tethering bar on the top. Below are some screenshots.