In order to detect sound frequency, I think Fast Fourier Transform can come in handy, although I must admit I have zero experience in that field.

Anyway with experience in the field of sound frequency detection?

This could be a start point to some apps like the following:

http://www.youtube.com/watch?v=oIpK6...layer_embedded
http://www.youtube.com/watch?v=BvrMNApVCQE

I guess that the people with this kind of knowledge won't spend time developing this kind of silly apps but this could expand our apps arsenal and target a wider set of potential users, so if anyone knows of a python binding for numpy.fft for N900 or something similar, posting here his experience would be a nice start.