The listing, Google Voice Invite has ended.
I will forward you the unused invitation email.
From the Google Voice Website:
One number for all your calls and SMS
* Call screening - Announce and screen callers
* Listen in - Listen before taking a call
* Block calls - Keep unwanted callers at bay
* SMS - Send, receive, and store SMS
* Place calls - Call free within the continental US and to Canada
* Taking calls - Answer on any of your phones
* Phone routing - Phones ring based on who calls
* Forwarding phones - Add phones and decide which ring
Voicemail as easy as email, with transcripts
* Voicemail transcripts - Read what your voicemail says
* Listen to voicemail - Check online or from your phone
* Notifications - Receive voicemails via email or SMS
* Personalize greeting - Vary greetings by caller
* Share voicemail - Forward or download voicemails
Voicemail as easy as email, with transcripts
More cool things you can do with Google Voice
* Conference calling - Join people into a single call
* Call record - Record calls and store them online
* Call switch - Switch phones during a call
* Mobile apps - Try our apps for Blackberry and Android phones
* Mobile site - View your inbox from your mobile
* GOOG-411 - Check directory assistance
* Manage groups - Set preferences by group