For Cessna aircraft performing flight test operations, the aircraft N number is not used. Each test pilot is given a unique number, so a call sign would be "Cessna Test 41". The 41 is the pilots number, and not related to the aircraft. Therefore the pilot may use the same call sign for years, regardless of the plane he is flying. This is done because the test pilots fly various aircraft, and it alerts ATC as to the nature of the flight.
Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.