Google Voice Overview
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I got an invite to Google Voice last week and played with it for the first time today.
Overall, I was really impressed with the UI and ease-of-use. Though it is possible, I didn't play around with making outbound calls with GV. The benefit for me is integrating SMS and voice conversations in a web app. The voicemail transcription is killer. When a caller leaves a voicemail, the message is transcribed and text messaged to you.
Privacy will be the main concern for some people. For me, it's not an issue. Big brother GOOG already has access to my email through Gmail, my documents through Google Docs, my purchases through Google Checkout, and countless other services I subscribe to. There are always sacrifices for convenience, privacy is one of them.
Here's a good review on Google Voice from TechCrunch.