AT&T has announced availability of tethering for the iPhone and sweeping changes to their data plans. The current $30 unlimited smartphone data plan will be replaced with two new plans. DataPlus will give you 200MB for $15 per month and DataPro will give you 2GB for $25 per month. Overage charges have changed as well, customers with the 200MB plan will be charged $15 for each additional 200MB while customers on the 2GB plan will be charged $10 for each additional gigabyte. Current customers of the $30 unlimited plan will be grandfathered in but can switch at any time.

Tethering is finally coming to the iPhone on AT&T and will be offered as an add-on to the DataPro plan for $20 extra per month. The additional cost to add tethering sounds reasonable but 2GB of shared data sounds a little on the slim side. However, compared to the $90 you’d spend on iPhone data and a 3G adapter for your laptop, it’s not too bad a deal.

The final change is that the $30 iPad unlimited data plan will be replaced with the same $25/2GB smartphone plan.

All of these changes will be taking place on June 7, except for iPhone tethering which will launch when iPhone OS 4 does.

I suspect these changes will benefit the vast majority of users, I would consider myself a heavy data user and I’ve barely used 2GB of data in the past 4 months. I’m not happy that this is the end of honest to goodness unlimited data, but I’m glad to save a few bucks every month.