[citation][nom]JimmiG[/nom]Maybe Apple knew about the antenna problems before the phone was officially released, but didn't have the resources to re-design it?[/citation]
The Antenna doesn't need to be "re-designed". If you're going to look at a good neutral-ish source, Anandtech reviewed the iPhone4's antenna to suffer the "death grip" phenominon when your touch bridges the 2 external antennas, but showed that this results in drop calls only if the signal was very weak to begin with... the iPhone4 does a great job of hanging onto a weak signal so long as this doesn't occur. Other sources suggest that you can shield the sensitive area with solutions as simple as a piece of scotch tape.
Apple just clearly didn't test the device enough under low signal conditions to identify the problem, since it'd be really really cheap to fix.