Google Voice is a new feature from Google. Currently, that is still available by invite. I have watched some video clips about its features. Yes, Google Voice has a voice mail feature and you can listen your voice mail online. That is a lot of VOIP applications have this feature. I have used Skype Voicemail around 4 years ago. But it can do voice to text. It can provice a voicemail transcription to your Gmail and sms too! That is great, it makes all your voicemails are searchable. Today, I read Google offical blog, you can bring your own mobile and binded with Google Voice(but I think that is US only).

Reference Links:
Google Offical Blog
Google Voice Video