Like was demonstrated earlier (And later taken offline by Apple) the Verizon iPhone has a different antenna design than the GSM version. Above is AT&T’s design. notice the breaks in the antenna on top…
And on Verizon’s below there are no antenna breaks at the top but instead on the left side:
Tim Cook said as much in the QA:
Q: Experience is so paramount at Apple… GSM allows data and voice… how does that experience feel here?
Tim: I think people place different emphasis on things — I can tell you that the number one question I’ve gotten is when will the iPhone work on Verizon. I couldn’t be happier to tell people that. They will make those sorts of tradeoffs.
11:24AM From us: What changes if any have been made to the antenna.
Tim: We had to make changes to work on the CDMA network — it’s going to work great.
Dan: We do not see a problem with that. (We’re assuming he means the antenna)