My Cessna 150 had a short tail number.  N35TD.  I was routinely asked for my
"full call sign" but it wasn't a problem at 150 speeds -- the controller
could probably finish several cups of coffee before I got near his traffic
pattern.  But they do expect a five character call sign, that's for sure!

And then there was the day that "Cessna three five tango delta" and "Baron
five five delta tango" were both doing practice IFR approaches with the same
controller.  What a fiasco that was!

Rick Argente said it well a few years ago -- the tail numbers may look good
but you should say them out loud a few dozen times before you paint them on
your airplane.  After all, you'll be saying those words more than most others
while flying your airplane.

- Rob Wolf