Currently unlimited data plans for existing iPhone and iPad customers are still in effect. However, once contract renewals come up, don't be surprised if you have to wave bye-bye to unlimited data. The press release did not say if the $20 tethering option would be available to those who decide to keep their unlimited data for now, but MacRumors believes tethering won't be available unless you're on the 2 GB "DataPro" plan. Unfortunately, they're probably right. Update: They're right. Tethering is only available as a buy-up from the DataPro plan, and is not an option for grandfathered unlimited-plan users.
The new data plans take effect June 7.