One time I was at the gate and missed the boarding call.

To be clear, it was Terminal F at PHL--all USAirways express flights. As is customary in Terminal F, the gate for my flight had been changed four times. As is also customary, announcements for the gate at which one is waiting in Terminal F were nearly inaudible, although boarding calls for Terminal A-West (international flights) came through loud and clear. This always makes me wish I were going to London or Paris or Munich, or pretty much anywhere except where I'm supposed to be going.

I heard the announcement for zone 1. I'm nearly certain that there were no more boarding announcements for my flight, either for other zones or for final boarding. It is possible that I failed to hear announcements that were made, but what I think happened was that, as zone 1 passengers were boarding, all the rest got in line behind them and the GA thought that no further announcement was necessary.