I'm divided on it. To get the old 5GB ("unlimited") a month plan would cost $20 more ($50 total instead of $30). However, they are making it possible to lower peoples bills now. Before this, no matter what data cost $30 a month on 3G for the iPhone. Now, people can shrink that down to just $15 and be fine. I checked my iPhone statistics, going back to July of 08, and I've used an average of 245mb a month. My first month with the iPad when I was intentionally using certain things heavily, I still only hit 389mb. That will go down quite a bit, as WiFi at our new office is finally coming online in the next week or two.

It's also good to see AT&T being way more proactive in notifying users when they are approaching their monthly limit. Having warnings at 65%, 90% and 100% should help to avoid the surprise of overage.

I can partially see AT&Ts side on the tethering. Data usage on a phone, or even an iPad is going to be less then data usage on a laptop. My phone and iPad aren't constantly downloading OS X/Windows updates in the background (with sizes sometimes rivaling my monthly usage just to update iTunes). I'm not pulling down tons of flash, 720p Youtube videos and so on. So that part I understand. However, charging $20 extra is what I'll disagree with, especially since it doesn't even add any data. If I burn through my 2GB in a month, then start charging me overage.

As for what T-Mobile or others will do, it's hard to say, but the industry tends to follow each other closely. Charging for tethering is pretty standard unfortunately, and I doubt most carriers are pleased with Google tossing it into 2.2 without having each carrier enable it. It will be interesting to see what happens there.