, users of unauthorized tethering apps, such as MiWi, are receiving letters that present two options: stop tethering, or start paying $45 per month for a DataPro smartphone plan, which includes tethering.

Tethering allows users to let laptops or other devices use a smartphone's data connection, either by USB or Bluetooth. For this service, AT&T charges $20 per month on top of its basic 2GB, $25 smartphone plan, and gives users an extra 2GB to play with.

But , users who jailbreak their iPhones -- that is, install a hack that allows the installation of apps from outside the iPhone App Store -- have been able to circumvent this policy with unofficial tethering apps, such as MiWi. The letter effectively warns these users that the free ride is over.

"We've noticed your service plan may need updating," the letter says. (I love the passive-aggressive tone there.) "To take advantage of this feature, we require that in addition to a data plan, you also have a tethering plan. Our records show that you use this capability, but are not subscribed to our tethering plan."

Users who continue to tether will be automatically enrolled in the $45 per month plan, the letter says. For users who are plan, this will also put them onto a capped data plan.