Why do airlines use separate call signs instead of using their IATA/ICAO codes?
Example If you want to say "Uniform Alpha Lima 425" is easier than saying "United 425?" That doesn't seem easier at all. If fact, it seems harder. It might make the training easier, but does it need to be easier? The job is pretty tough and a fairly simple way to cull the herd seems to be taking out the folks who can't remember call signs.