Originally Posted by
safelife
Who says an aircraft can't SELCAL another. Many ways exist, SELCAL tone coders for Windows, iOS, android are available.
In fact I have retrieved at least two "lost souls" over the Atlantic (one with Iceland, one with Gander, both were happy to provide the code) exactly like that.
While it may have worked for you, the combination of the frequency response of the iPhone's speaker and that of the aircraft microphone would mean that it could not be relied upon for any more than marginal reliability. Therefore not designed-in to procedures. Real encoders are wired directly into the modulator.
I wouldn't mind betting that aircraft modulation circuits have frequency response shaping to roll off the high frequencies of white noise found on the flight deck, thus causing more of a 'twist' between the two tones. Did you guys really believe that macho voice was all yours without artificial help?