You're saying that AT&T would have no objections if you downloaded the entire internet to your iPhone, but if you share the connection with another device they'll cut you off?
Every ISP have a bandwidth limitation before they consider you as disruptive to their network (which is the word they use in their TOS). Downloading the entire internet over 3G for the whole month is fine as long you're not downloading them in one day on two or three different devices.
Do you have any proof AT&T will care? Not trying to call you out or anything but I use to tether my iPhone to my laptop to download torrents since my dorms last year blocked it. I downloaded at least 50 gigs and never heard anything from AT&T. Also if you're worried about battery life I'm thinking the camera connection kit will also charge the attached iPhone but I have no way of knowing for sure.
I have known people who gotten calls from AT&T about this, and often get warnings from them before AT&T cut them off for "disrupting the service". It's not about how much stuff you download, but how much bandwidth you suck from other users on that cell network near you. Disruptive is the keyword here. People bitching about dropping calls and slow internet is much more an issue for AT&T than the tethering and jailbreaking. They rather cut you and lose customer than to lose several more.
I've never been able to getna straight answer out of anyone regarding whether or not sharing the iPhone Internet connection actually violates the service agreement. The wording about usage is vague. My interpretation is they have the right to kick you off their service for whatever use they deem inappropriate, but there is no current case law where they have actually sued anyone.
I talked at length with the manager of my AT&T store about this. Her posititon was that jailbreaking voids the phone warranty but not the service agreement. Of course, that conversation does nothing to protect me from losing my service nor getting charged for overuse. I just thought it was interesting. She also said that someone higher up the food chain too her they would be offering a pay as you go tethering "plan" within the year. That dashes my hopes of AT&T just turning the feature "on".
All I can say is I have used tethering and downloaded copious amounts of data on AT&T with the iPhone and Sprint with the Treo, and I haven't seen anything unusual on either bill.
These are just observations for the sake of rhetoric and NOT legal advice.
Jailbreaking is not the issue here, it's the bandwidth. AT&T doesn't care about you jailbreaking your phone, that only applies to Apple.
The bandwidth you suck down daily does impact the bandwidth availability for other people on the same cell tower that you're connected to. Being disruptive to others is what AT&T doesn't want.
AT&T doesn't need to sue anybody, the disruptive is in their TOS. You agreed to that, therefore you have no legal grounds to sue AT&T for cutting you off.
