Back when I had a Storm 1, the Crackberry forums had all kinds of posts about tethering. I interpreted the various posts as saying that if you tether, you are in violation of the VZW terms of service. I also learned that most folks felt that if you tethered occasionally and, in particular, avoided streaming and other high bandwidth activities, VZW probably would not be interested in going after you. Of course, no guarantees.
My view is that as long as I tether to merely check a few emails and the like occasionally, I am ok. While VZW, cadres of attorneys, and some able learned participants in this forum would disagree with me, I feel I am not violating the terms and the spirit of the terms of service.
What VZW really wants is to get $30 per month from you for tethering. Period. In the past I have sometimes paid this fee to obtain the tethering rights legally for business purposes. One gripe that I have is that while VZW has a number of things you can change online, tethering is not one of them. You have to call customer service and go through the hassle of finally getting to someone who can help you and ask the service be established. You also have to call to turn it off. I wish they would make it easier to do this.
But, what really gets me is that if I tether and use 250mb in a month to check emails here and there, how does VZW feel if I go through 1gb in a month for sites like tv.com on my Droid? The former ostensibly a violation and the latter within the rules.
All in all, I say that if you do choose to tether, no matter how little you use, you are at risk. Perhaps a small risk, but a risk nevertheless. Just how they can find this out is beyond me. I seriously doubt they can get anything out of my router that proves anything. They would have to look at daily/monthly use rates attempt to identify statistical outliers to suspect anything. For those of you who would tether and stream like there is no tomorrow, I say you are at high risk.
Regards,