FlashArmyKnife in the iOS App Store has secret built-in powers that will allow you to tether you iPhone to a computer for no extra charge. The app costs $2, while using your iPhone's data connection on a separate device would cost you a monthly fee.
As we said before, the app's tethering capabilities are secret so you'll need to enter a Konami Code-like cypher from the app's trigonometry calculator to get the tethering to work. The instructions in video above have everything you need to know.
Go to calculator in F.A.K. Enter following without commas:
1642, M+, C, 1452, M+, C, 1943, M+
When it says "run", tethering is running. Press "C" to stop tethering.
The apps people at Apple are all currently on vacation, and iTunes Connect will be completely down until Friday so, presumably, FlashArmyKnife will just chill in the app store until then. That said, if you're interested in giving it a shot, now's the time to go.
Warning: While we know the app's tethering works for some, we can't be sure it's not some sneaky under-handed way of getting at your personal information or that it'll necessarily work for you. But the developer Eric Blase seems to be relatively open about his identity for whatever that's worth to you. [iTunes]