Current iPhones Keep Cheaper Plan on Reactivation
tidbits.com/article/9680
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
You won't pay a 3G rate for a 2G iPhone with a new service plan, AT&T confirmed for me today. This should be good news to anyone looking to either sell their so-called 2G iPhone when they upgrade to an iPhone 3G, or for those looking to buy (or beg) the older iPhone model without paying a fee for bandwidth they can't use.