Yes, the voice of Siri has been unveiled on CNN as Susan Bennett from Atlanta.
She is a voice-over professional who was initially employed by a technology company in 2005 to record herself speaking random sentences and phrases for hours and hours each day.
These recordings were cut up into small parts (vowels, consonants etc..) and are used in combinations to create every word that Siri is capable of.
She had no clue that one day those clips would be used on the iPhone, in fact she didn't even know what an iPhone was at the time!
I watched an interview with her on TV, it was very interesting actually.