From Google blog:
Google Voice is a service that gives you one phone number to link all your phones and makes voicemail as easy as email. If you requested an invitation on the Google Voice site or previously on GrandCentral, keep your eye out for an invite email.
To learn more about Google Voice, check out the video below. If you haven't signed up for a Google Voice invite, make sure to get on the list by leaving us your email address at www.google.com/voiceinvite.
I use Google Voice widget as a contact tool on my biographical website and would encourage you to sign up for this useful and free service.
Nexus One - Google Voice