It looks like GV is unable to send SMS. Some have reported that it seems to be affecting only AT&T users. So if you are on AT&T you might not be getting SMS from GV.
Update 1: It looks like SMS aren’t being sent out or forward to mobile phones. This seems to be affecting other carriers and not just AT&T.
Update 2: It looks like someone from Google is looking into the matter. You can follow it at the Support Forums.