You think you're a real smooth criminal, don't you, using the Cydia app MyWi to tether your jailbroken iPhone free of charge? Well, it looks like your joy ride might be over. AT&T has apparently been sending MyFi users texts telling them to pay up or fall back:

AT&T Free Msg: Did you know tethering your Smartphone to a computer requires a tethering plan? Pls call 888-860-6789 for details or visit att.com/dataplans.

Subsequent emails alert unauthorized tetherers that if they continue using the feature without opting for the upgraded plan, AT&T will just go ahead and do it for you:

If we don't hear from you, we'll plan to automatically enroll you into DataPro 4GB afterMarch 27, 2011. The new plan - whether you sign up on your own or we automatically enroll you - will replace your current smartphone data plan, including if you are on an unlimited data plan.

If you discontinue tethering, no changes to your current plan will be required.

It was a good racket while it lasted. But the real mystery is how they're detecting it. Traffic patterns? If you have thoughts, speak up in the comments. [ZD Net]