Can you skip it? If you cancel is the phone activated anyway?
Not sure why it is prompting this if your account has an iPhone data plan.
Either way, see above, you are still grandfathered w/ the $20 plan.
I don't know why he is being prompted to downgrade to the 2G data plan. I have never once had to do that when using my 3G sim in my 2G iPhone. I just tried it myself in my post above. My data plan is still a 3G data plan.