Go to the main FSX directory and search for a .cfg file named "airlines". There are the callsigns ATC use, so add "Speed Bird" for BA (Note: "Speedbird" won't work), "Japan Air" for JAL, etc. Do not remove the original callsign "British Airways" or "Japan Airlines" from the .cfg until you select the new custom callsign at least once with your flight or you will get the error: "British AirwaysSpeed Bird" or Japan AirlinesJapan Air" even if the are not there anymore.

Good luck

Hi Jazz777

You should open the aircraft.cfg file with Notepad. The file is located in <FSX Root Folder>\SimObjects\Airplanes\CS_B757-200. If you installed FSX in the default location, you would find the file in C:\Program Files\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\CS_B757-200 or C:\Program Files (x86)\Microsoft Games\Microsoft Flight Simulator X\SimObjects\Airplanes\CS_B757-200 if you use Vista/Windows 7.