One thing that has always been the nirvana of data collection for companies has been call centers. About 7 years ago a company I worked for had a product called Behavioral Analytics. The genius of this system was that recorded conversations with agents would be analyzed for the mood and other elements. With the voice vs. just text you are able to detect so many different attributes of the person. This all had to be done offline due to the amount of computing power needed.
Today with the advancements of clusters of transcoding servers all this can be done in real-time and time, providing hits to the call center agents on what to do next. Imagine all this being done at a small company without the billions of dollars that Google has to make your customer experience better on the phone.
Now image Google doing this? They have the processing technology and dollars to take every call made with Google voice, identify the parties you are speaking with, build in your emotional state, and provide advertisers even more data points that are used to market you as a person.
I am sorry there is just something that feels wrong with using Google as my phone / voice messaging platform. But this is a free market so people can make their own decisions on what they will use. For me it's not Google, I am happy running my own VoIP server at home with no Google interaction.