This appears to apply to all phones, not just the iPad/iPhone. They have also, as expected, introduced a tethering option. The tethering option is very limited however; it appears to have a 2GB limit.
So in the old days $30 got you unlimited data, but now $45 gets you data, tethering and a 2GB limit. Forget watching YouTube on the AT&T network.
There's no word yet on whether Apple will introduce some smart metering features to help track usage with OS 4. I hope they will. AT&T will send out text message notifications.
Everything about this announcement is exactly as expected -- including the fairly onerous pricing with tethering (I'd have been very impressed if they'd gone to tiered data plans and made the tethering free -- it's just data. This is AT&T however.)
So what's the bright side?
AT&T has been selling capacity they didn't have. I'd love to see a zillion dollar fraud prosecution. Now, finally, that stops. They will be aligning their pricing with their network capacity. There's now hope, for the first time, that we'll get reasonable voice service on the iPhone.
It's also good that we have more price transparency -- we are more likely to get what we pay for, and see what it costs. If we don't like the price we can .... ummm ..... uhhhh .. stop watching videos on the AT&T network. (Note VOIP services use far less bandwidth than video. I wonder about dropping our family plan to the rock bottom minimum and using Skype to call Canada. I tried their online usage calculator, and, as expected, with no video use, I still need the $25 plan.)
Overall, this is good. Painful, but good. Now about my share of the class action lawsuit for AT&T's fraudulent overselling of their capacity ...
Update: AT&T's tethering pricing is pretty nasty, but there's some good news on pricing details that resemble the iPad 3G plan:
... AT&T has also overhauled their data overage structure, giving DataPlus subscribers and additional 200MB as needed for $15, while DataPro users get extra data at $10 a gigabyte... if you’re either over-using or under-using your plan, AT&T’s going to be extremely flexible about letting switch back and forth between DataPlus and DataPro. You can call and have your plan changed at the next billing cycle, have it prorated immediately, or - hold on to your seats - have the plan retroactively applied to the entire current billing cycle...The $10/GB rate makes the tethering more practical. Definitely more complex, but I wouldn't be surprised if AT&T's accounting system can't support a finer grained process. If Apple bundles a good metering app with OS 4 this new plan would be an improvement for my family. (I wonder if Apple/AT&T will consider selling an iPhone without a data plan ...)
Also, there's rumor that AT&T has said that current users can keep unlimited data when they get a new phone and new contract. I find that hard to believe.
Update 6/10/2010: The new contracts come with a secret 8 month old catch. Ohhhh, AT&T is evil-incarnate.