I've had dropped calls on my iPhones (3G & 3GS). Inside an elevator or while walking through a tunnel surrounded by 2 metres of concrete in an underground carp

I've had dropped calls on my iPhones (3G & 3GS). Inside an elevator or while walking through a tunnel surrounded by 2 metres of concrete in an underground carpark...Never at any other time. This is from using it in 3 different countries (none of which was the US). I think I concur with your conclusion.