Hi,
just for your info, the company I work for at Exeter, Celtic West, has it's own ICAO identifier, CWE and callsign, Celtic.
We are allowed to use this for all of our flying activities:
so for our charter flights we use the callsign CWExxy (x being the date of the flight, and y being which leg of the charter eg. CWE031A),
CWExT for our PPL, IMC, Night and Twin training (each instructor has his own number)
CWE0x for non commercial flights using our aircraft (again each pilot has their own number).
Not sure if the above helps but it may be of interest.
We have had the code and callsign for about 4 years, but have to be careful sometimes as EuroCeltic have their name as their callsign (I beleive we had ours first, and were a little concerned that permission was granted for theirs), and another similar sounding name Celtic Airways of Plymouth were trying to use "Celtic" for themselves.