This would be a great news for people who have already got a Google Voice account (At the movement it is invitation only). Google voice is a simplified great concept to manage all your phone number under a one number as well as to hide your mobile or any other phone number. Also it would be a good solution to stop or avoid calls that you do not want.
This is new Gmail Lab feature that will allow you to receive Google voice messages and play them on the same page.
"Previously, clicking "Play message" opened a new page in your browser, but starting today, you can play voicemails right in Gmail. Just turn on the Google Voice player from the Gmail Labs tab under Settings and whenever you get a voicemail notification, the player will appear right below the message itself." Says in Gmail Blog.
Official Gmail Blog: New in Labs: Play Google Voice messages in Gmail
