I sometimes pass depending on what I'm wearing and who I'm with. Recently I've passed most of the time, and for some reason, my voice hasn't given me away yet. I find my voice painfully girly, but apparently others think it's in line with the 12 year old boy that I look like. So glad I'm lucky enough not to have a give-away voice.
Then again, I still haven't been kicked out of the women's restroom yet, so maybe I'm not passing as well as I think XD I've gotten a few funny looks but nothing more. Still need to build up the courage to go to the men's.