It looks like US mobile operator AT&T may be cracking down on iPhone users who are using tethering on their jailbroken iPhone, and using unofficial applications to turn their iPhone into a WiFi hotspot.
These unofficial applications have been around for a few years, but with iOS 4.3 you can now officially use your iPhone as a WiFi hotspot, of course to do so will involve an extra charge for your carrier.
A number of iPhone users who have been using unofficial tethering apps are now reporting having received text messages, followed by an email, which says basically says that AT&T knows they are using tethering but not paying for it.
You can see the full email over at Cult of Mac, as well as some screenshots of the text messages sent out to iPhone owners.
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