It's called "MediaNet Unlimited" and it's $15/mo per phone.

Wow. I just looked at the MediaNet plan for GoPhone. $4.99 per month gets you 1 MB, with each KB costing $.01 thereafter.

As much as I stream last.fm with Vagalume, I'd need to win every lottery in the US

The thing that's confusing with AT&T is that their DATA PLANS are only for the "smart phones", like Blackberries, Treos, whatever. Consumer cell phone uses MediaNET which is supposed to be the drivel AT&T provides such as their sites for buying ringtones, backgrounds, games. It got a bit better with an HSPA phone, because I can watch selected TV shows, and do some browsing. I tried installing Opera-Mini on my Shine, but you have to zoom in to see anything.

The way I read the ToS, tethering a computer to a smart phone is what AT&T doesn't like. Since consumer phones are "locked down" by AT&T (you can't delete the dumb demo games they put on there, for example), the fact that tethering via bluetooth works indicates (to me) that it's not THAT important to them.

As always, you sense of what's right should be your guide.