Some General Aviation pilots use their aircraft registration as a call sign, like C-ADYDJ for example. I've heard some use their aircraft type then some numbers like Cessna 45G. Then the typical airliners who use their company name then flight number, like ACA783.
When are you required to use your aircraft registration, and when are you allowed to replace it? If you are allowed to change it, can anyone use whatever call sign they want or is it limited to airlines only?