If you are currently on the $30 iPhone data plan you can keep it as long as you want even if you are eligible for a new iPhone 4 upgrade. You will however lose the $30 plan if you want to tether your iPhone.
AT&T now has 2 data plans to chose from, Data Plus and Data Pro. If you want the tethering option, which will cost you another $20, you have to ditch your unlimited $30 plan for the $25 data pro plan. Data Pro offers only 2GB of data per month. All new customers will only have the Data Plus or Data Pro option.
Now, iPhone 4 hardware pricing.
AT&T customers: To find out when you can upgrade without a penalty you can dial: *NEW# on your iPhone which will generate a text message telling when you can upgrade. AT&T bumped up a lot of people to an early upgrade. They are taking off up to 6 months so be sure to check to see when your contract ends.
If you contract ends after January 1, 2011, you can still get a discounted price but you will have to renew your contract another 2 years still. If you do not want to renew your contract you can buy the iPhone 4 with no commitment. Please see the pricing below:
iPhone 4 16GB with NEW or eligible upgrade $199
iPhone 4 32GB with NEW or eligible upgrade $299
iPhone 4 16GB with upgrade date after January 1, 2010 $399
iPhone 4 32GB with upgrade date after January 1, 2010 $499
iPhone 4 16GB with no commitment $599
iPhone 4 32GB with no commitment $699
The iPhone 4 will be available for preorder on June 15 and in stores on June 24th.