captain cumulonimbus
In my experience the use of callsigns instead of their associated trigraphs comes down to experience. The more time you sit in the seat and use them, coupled with your professional pride and application, the quicker you start using them properly. The same can be said for filling out paper flight strips. I used to see many controllers waste valuable scribing time by writing out the callsign in full on the strip, such as Speedbird 123 when writing BAW 123 would have saved a little time. This small amount of time spent here all adds up when you are dealing with multiple freecalls.