Meet Susan Bennett, the voice actor whose work became the original voice of Siri—for the record, my internal jury is still out on Siri's new voices in iOS 7. In the video below, you can hear elements of Siri's speech; at the same time, you get the tiniest glimpse of the monumental effort it takes to turn recordings of nonsense strings of words into a synthesized voice, because Susan Bennett and Siri are not exact matches. As a voice actor paid by the hour, Ms. Bennett didn't know what she was being hired for by Nuance (the Dragon Speech and Dragon Dictate folks) in 2005. She didn't find out until until 2011—when Apple released the iPhone 4S and Siri—when "a colleague e-mailed me [about Siri] and said, 'Hey, we've been playing around with this new Apple phone. Isn't this you?'" CNN's companion article also has some interesting info.
Check It Out: Meet Susan Bennett, the Voice Actor Behind the Original Siri Voice