Originally Posted by
Alan Baker
A callsign is only ever spoken that's why it's called a callsign. In normal operations you would never see it written.
Of course it's written! ICAO Document 8585 is the canonical source which lists them in written format in a phonetic manner designed to be pronounced exactly as shown ( refer to Dave's response about AIRFRANS above ).
How
do you think controllers learn to pronounce a new callsign...?