"How many legs does a dog have if you call the tail a leg? Four. Calling a tail a leg doesn't make it a leg." -- Abraham Lincoln
In other words, you cannot change a man's voice in to a woman's: no matter what transformations you do to the sound, it will still be a man's voice. There are no unique characteristics of "men's voices" versus "women's voices": there are only statistically significant variations.
You would probably find it a lot easier if you were to restrict your scope to the well defined, such as doing pitch conversion.
