If you signed up with Gmail to be notified of any “invitations”, Gmail should have sent you a “welcome” email with an invitation. Google is expanding its invitations in huge numbers to people who signed up with Google to be notified of any updates. This may be an indication that Google may open the doors the service to anyone pretty soon. However, as Google is famous for its “beta” naming and limited test releases, that “pretty soon” state may be a few weeks, or even a few months, away.

For people needing more invitations, there are 50 Gmail invites, which keep refilling by themselves, available to anyone who lets me know their email address to send the invitation to.