I find it personally appalling that every guru out there, skips over this subject or touches on it and rolls over it like its no big deal.
Tonality is equally as important as bodylanguage in my opinion. If your nervous, where does it come out. In the tone of your voice.
Example: The other day i was joking with a girl and made a bet with her that I promptly won, she promised to pay me back. The next day I see her im in control of the conversation, my tone is good, and i joke so wheres my five bucks and all of the sudden I see her mom come right over the top of her and she says, "I dont like my daughter owing anybody any money. She doesnt owe you anything." In my head I was competely knocked off my kilter and where did it show: In my voice. I spoke in a higher voice, it wasnt smoothed over. I talked in spurts. I tried to explain to the women it was a joke, but my voice was one of distrust. It was not one of control or power and she went right over the top of me and I ended up just walking away from her.
A man whose in control of his emotions (alpha male), talks slowly, puts pauses to add suspense and most importantly talks in a deep voice. I find when ever Im in the zone my voice gets deeper. My voice slows down. If you watch some of the actors women like the most. The have a rumble to there voice or some quality to there tone that seems almost magnetic.
Good tonality is good in every stage. Attraction, qualifying, comfort and especially seduction.
Personally I find tone as important as eye contact, if not more.