Why is there a beeping sound when I make a phone call and not any other sound?

This sound is called "ringback tone", and it is the sound that the caller hears from the phone after dialing a number, which is not the same as the national standard, but it is similar.

This is the sound that should be used by all telephones in the world, and it is possible that 440Hz was chosen just for A, but it is more likely that some of the signals are at this frequency, and the reason why the transmitted signals are at this frequency is because of quality, efficiency, and so on

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