First, there was Google Voice.And all was good, and not so good.But it showed that there is a better way to manage voicemails than to listen to 15 in a row just to get to the one you care about. Now, there is an alternative to Google Voice called Ribbit Mobile.And it too is very good.Ribbit Mobile is in private beta, but the first 500 people to sign up with the invite code techcrunch will jump to the front of the line.Ribbit Mobile starts out by taking over your cell phones voicemail.You give it