The front and back of Apple's iPhone 4 are composed of glass. Photo: Jim Merithew/Wired.com

With some unauthorized hacks, you can share your smartphone’s internet connection with other devices, free of charge — and AT&T has had enough of that.

On the iPhone, for example, the hack MyWi has been a popular tool for “tethering” the handset’s internet connection for free, and just recently users of MyWi reported receiving text messages and e-mails from AT&T requiring them to “update” their plans.

“Well, that was fun while it lasted,” a MyWi user posted in a forum. “It was a good 3 years. Goodbye iPhone tethering.”

AT&T is telling users of free tethering that they have three options:

1. Stop using free tethering.
2. Contact AT&T to activate a legitimate tethering plan and start paying up.
3. Go ahead and keep tethering, and AT&T will automatically sign you up for a tethering plan and bill you.

Also known as mobile hot-spotting, the official tethering service provided by both AT&T and Verizon costs an additional $20 per month on top of data and voice plans. Free, unauthorized tethering has been accessible on the iPhone for years, and AT&T is only now beginning to crack down on people using the service without paying.

“We’ve just begun sending letters, e-mails, and text messages to a small number of smartphone customers who use their devices for tethering but aren’t on our required tethering plan,” an AT&T spokesman told Wired.com. “Our goal here is fairness for all of our customers.”

AT&T told Wired.com that it’s “able to determine if a smartphone customer is using the device as a broadband connection for other devices,” which isn’t surprising, because telecom carriers carefully monitor our mobile activities, counting the number of texts we send, voice-call minutes placed, and data used per month.

It’s unclear whether Verizon will take similar action on smartphone customers using free tethering tools. Verizon did not immediately respond to a request for comment.

Wired readers: Take our poll! If you’re an AT&T customer and you’ve been tethering with your phone, we want to know whether you’ve heard from the carrier about it.

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