Random? No. AT&T's been trying to crack down on the practice lately, firing random e-mails at users who aren't signed up for tethering, but whose accounts show higher-than-normal usage for smartphones.
I doubt they're random, I use 10-20GB a month because I stream video all the time through the iTunes app (podcasts). I've never jailbroken my phone though. No letter or threats from AT&T, though I also have several FCC complaints on file against them as well already, so that could be another reason.
Next Bill Cycle: 05/14/2011
Data (MB): 14252.1 of Unlimited
Messaging: 5841 of Unlimited
SeleniaI love DebianPremium
I only ever tether in an emergency, which is very rare. That being said, I use lots of data over my native smartphone apps and not a peep from AT&T.
San Antonio, TX
reply to goodcow
Im using about a gig per day just by streaming netflix on my iphone. Thank you grandfathered unlimited plan.