First its only available in the united states, and that sucks because i'm not, you log in and choose a Google number, it becomes your online number, you add all your phone numbers on the account ( home , cell , etc ) any calls received will be sent to all phones ( i think ) but thats not the best part, you can make phone calls to any number in the united states, and Google will forward it to your phone, meaning Google will call both you and the one you want to call then put you two together. i think its working already, and you don't need any invitations, just a US local cellphone number.
~Coalwater~