I just got back from AT&T where I picked up a new iPhone 4 for 3rd line. The phone came in yesterday and still has the antenna problem.
As I mentioned elsewhere, I wouldn't hold your breath waiting for a replacement with the antenna fixed. Obviously the problem has to be fixed, production has to be changed to incorporate the fix and since it involves an antenna used to transmit RF, it may need FCC approval before Apple can do anything else with it.