From the article: How Google Voice Works?
Google Voice gives you a free number and many interesting features, including the free transcription into text of your recorded voice calls. But Google stores your call transcripts in a huge database that can even be indexed on Google's web searches. Also, other parties like hackers and mandated government officials can access your personal data. What would you do about it? Stop using Google Voice? Use it, but be careful about what you say on the calls? How about requesting encryption, and re-defined the security issue in the Google Voice service? Throw your two cents.