Apple changed the antenna design in the iPhone 4 Verizon variant, and in the 4S to really resolve the issue.
That fixed the actual problem in hardware - the software fix just made things look better.
That fixed the actual problem in hardware - the software fix just made things look better.
All my iPhones, not just the 4, regularly dropped calls with AT&T until I switched to Verizon.
The software fix made things look worse. The "bug" was that the number of bars was misleadingly high.