All utterances made in the entire world have been catalogued within a 400 phoneme range. The majority of languages use a 40 phoneme range, and the most widely spoken languages fall within an 80 phoneme range.
which makes absolutely zero sense. Anyway, I was wondering what indeed was the phoneme count for the average language. One source is UPSID, and I've just found out that it's available online here on Langmaker, a site for conlang creators. There is a phoneme inventory index of UPSID languages with the phoneme count for individual languages. Lowest are Mura and Rotokas with 9 phonemes, and highest is Ga with 241. The mean is 30.26 phonemes, if my calculations are correct, with the mode being 26 phonemes, represented by 23 out of the 317 languages included.
a list of resources for conlang creators, also by Langmaker. Lots of materials about natural languages, though.
The Language Creation Kit, which has lots of good stuff about how languages, natural and constructed, work.