UPDATE: This requirement is only for those who purchased after 5/27/2008 and are turning their old iPhones in to get a new "free" (now with more expensive data!) iPhone 3G. AT&T employees may now uncross their legs.
This better not be true.
I just finished an e-mail exchange with an AT&T spokesperson who told me that if you upgrade from your current iPhone to iPhone 3G at an AT&T store, you need to turn in your first iPhone to qualify.
It seems wrong, so the Macalope advises a wait-and-see approach. Please wait to knee your local AT&T representative in the groin until after this is confirmed.