The Distaff Sound
I'm willing to bet that the majority of commenters are (a) male, and (b) inclined to carry their phone either in their pocket or on a belt holster.
On the other hand, there is a large segment of the population who, when not using the phone for endless tapping on virtual keyboards or sharing their life story with everybody in earshot (seriously, when I was in the emergency room awaiting test results was it really necessary for me to hear the lady in the next cube dissing her daughter in one call after another?), place it in the bottom of a large bag containing the rest of life's necessities.
How are such unfortunates supposed to receive calls if not with an audible signal? Assuming, of course, that they ever remove the phone from their ear in the first place....