Google offers a free phone number, Voicemail transcription, call routing, cheap international calling and a bunch of other cool features with Voice. (Great video overview of Google Voice services here.)

Until now, the free service had been invite-only, but now students (and apparently faculty/staff/teachers/alumni — really anyone with a school email address — can sign up. The service now counts 1.4 million US users but will probably explode with the current offer.

Already Google is saying, “Update (5/17): The response to this has been higher than expected. It might take us a little longer to get you your invites — but sit tight, they’ll come as soon as possible.”

International service is expected at a later date.

In the post, Google said Voice is great for students, which it might well be:

We’ve found that Google Voice can be useful in many different ways to many different people. But one group of people that it’s especially well-suited for is students. We’ve heard college students in particular really appreciate getting their voicemail sent to their email, sending free text messages and reading voicemail transcriptions rather than listening to messages (especially handy while in class).

However, Google also must see value in hitting students that are about to leave home for the fisrt time and may be willing to use their Google voice number as their primary line.

Google is also expected to announce a fuller-featured VoIP service integrating its purchase of Gizmo5 last year.  In fact, part of the Google Voice setup also includes a link to “Gizmo” SIP services.  See screenshot below.