When you suck up too much data on your iPhone on AT&T, they will eventually throttle you, especially if you’re on a legacy unlimited data plan (and especially especially if they think you’re tethering through a jailbreak).
Want to know what it’s like to be throttled, though? As this video walkthrough by AppAdvice makes clear, it’s hell, a total nightmare.
Your ability to receive data drops all the way down to just 0.1MBps thanks to killiing the 3G connection and falling back to EDGE, which is what cavemen used for the Internet on their iPhones back in 2007!
The lesson here? If you’re going to jailbreak tether, either be judicious with how much you download while tethered, or pay AT&T the $20 for a Personal Hotspot to keep them happy. You don’t want to see your iPhone gimped like this.