It appears that after AT&T warned their highest data users last month, they are now going after the next level down of high data users. It certainly isn't too difficult for AT&T to determine if a user is tethering their smartphone since the browser and OS characteristics utilizing the iPhone connection are from a desktop computer.
If you are oblivious, iPhone owners on AT&T use jailbreak apps to allow them turn their phones into Wi-Fi hotspots and share their data connection with tablets, notebooks or other devices. I have used my rooted Droid for the past 18 months to tether to my laptop (at relatively low data usage rates ~ 2GB per month) with no issues. I'm sure that since Verizon and AT&T have added data plans and enabled tethering on the iPhone with a fee...they will start to look for abusers like myself and maybe you.
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