Absolutely! As Ceera I virtually never use the same voice in public that I use as my male identity. I do it well enough that a lot of strangers have talked to me extensively and not realized I wasn't born a girl.
Within minutes of putting on my makeup and wig, my voice shifts up about half an octave to an octave higher, and becomes softer and more feminine. The way I phrase things and the tempo and modulation of my voice is also carefully different in female mode, mimicking the speech patterns of women I know well. I don't even have to think about it any more. It tends to stick that way for half an hour or more after I dress down again to male mode, too.
I spent three months watching you-tube videos and studying audio and video course materials on how to feminize a male voice, before I ever tried to go out en-femme at all. To me, having a feminine voice is as much a part of my presentation as my wigs or my breast forms. I've been asked when out en-femme to allow my friends who know I'm transgender to hear my 'guy voice', and it's actually getting difficult for me to do it any more. When I do, they can hardly believe that voice came out of me. As a male, I sing base to tenor. But Ceera's voice is a definite soprano.
I realized that a lot of MtF drag performers and CD's don't bother to change their voices. And that's fine, if that is how they want to present to the world. But to me, speaking in a male voice while trying to appear feminine is as jarring a disruption as a Shakespearean actor performing in Hamlet or some other period play stopping in mid-performance and answering his cell phone, in a New York accent! My goal when I go out is to be the woman that I feel is a part of me, and to be accepted as that woman, to the extent that I can manage it. I can't do that if I speak, and people are looking around to see where the burly football player is hiding, behind that pretty girl.