I can't find the other thread, someone asked for info on GV and invites:
Google Voice is currently available through invitations only. To request an invitation, leave us your name and email address and we'll send an invite to you when they are available.
We're also gradually giving invites to existing Google Voice users to send to their friends and family. If you have invites to send, you will see a 'Invite a friend' link on the left side of your Google Voice page. To send invites, click the 'Invite a friend' link and enter the email address of the friend you'd like to send a Google Voice invite. We'll be rolling out invitations gradually, so don't worry if you don't see your invitations immediately.