My 4S is jailbroke and I have been using MiWi for tethering to my iPad when I'm at the cabin. Just this week I have received a text message, email and now a letter stating my service needs an upgrade for tethering. If I don't upgrade they will automatically change my plan and lose my unlimited iPhone data plan. I have the latest iPad. I've been tethering for some time now but with older iPads.
You should try TetherMe, but they might be detecting you're tethering by how much data you have been consuming. Use TetherMe as long as you don't use tons of data in short periods or too much more than your monthly average...you were tethering and they detected it, so their system works, and if you need the freedom to use what you want when tethering, you might consider just paying for what you get.