I asked this in Linguistics, but apparently nobody there wants to venture an answer; maybe this is a better place to ask it.
My ear is not good enough to tell via observation whether people speak in musical scales, which would seem likely for those with a good ear (talented musicians, and those few who naturally have perfect pitch).
For example, do people normally speak with a certain pitch, say a middle C, and then when they lower or raise the pitch of their voice for modulation, speak in other notes within the C major scale (or C minor, or what have you)?
If they do, do other people find these speakers' voices more pleasant than someone who, for example, normally speaks dissonantly, in a note between C and C#/Db and then uses non-harmonious pitches when varying the pitch of their voice for effect?
On a related note (no pun intended), are the fake/robot voices (Siri and such) calibrated to speak "on pitch" and in harmony with themselves?
Finally, in a more Sherlock Holmesy-type vein, would it be possible to guess a person's favorite type of music based on which scales they use in speaking (major scales = rock or pop, minor scales = blues, 7th or 9th = funk, exotic scales = jazz or classical, etc.)?