From all fem characteristics, I think voice is the most difficult to do. I have never planned at this point to try it. Do not know how has been your experience with this part of passing.
Recently I found this video about a guy how is participating in a show where imitators compete. He (yes, HE) imitates Shakira, and he did it so well that Shakira herself met the guy today while she was visiting Chile.
The video is in spanish, but you will appreciate how well this guy did Shakira´s voice.
http://www.youtube.com/watch?v=gUcH2...eature=related