iPhone 3Gs Upgrade from 3G and Data Plan Automatically Added?

Hi,
I have a question for you all. Right now, I am on an family iPhone plan with unlimited text add-on. I am qualified for the $299 32gb iPhone 3Gs Upgrade price. When I go to the Apple website to buy the iPhone 3Gs on the Apple Store website, I click on replace an existing phone on the account, I enter my phone number, SS, and all that info.
However, when I get to the option to select the phone, it wants me to add another iPhone data plan.
Just to be careful, is this already going to replace my existing iPhone data plan with the new iPhone data plan? (essentially, the same?)
Please see the screen shot. Has anyone experienced this?

Thank you
Paul

 

Thanks and a few more questions:
1) So, since this is replacing my existing data plan for the same data plan, my rate should stay the same? (Because I have a FAN discount right now on it, so my FAN discount should still apply after the new data plan is added and old one removed?)

2) I plan to do the upgrade at the end of July for that AT&T early upgrade exception price....Is there a deadline of when AT&T will end this "special program"?

Thank you!!!