Does anyone know of any kinda software to convert song/mp3'z/amr'z etc. into polyphonic ringtones?

Is there such a software ?

Not sure, but you want to convert to midi. Should be, but if it's free, doubt it.
Tried a search on Google?

nokia multimedia converter.. is good! i think this is what u r looking....
or try dbpowerAMP converter...
converts to wav!