Just a quick note - a colleague is now receiving repeated "here is your access code" automated dial-out spam from viber.com (a free VoIP Skype-competitor) even though he has never used the service. I assume someone, for some reason, is using his office phone number to register for the Viber service on their iPhone or Android phone.
Having wasted 20 minutes wading through the gushing Viber.com website, it seems there is no actual personal support for the service at all. The 'Help Desk' is actually just a few web pages of how to set the service up.
As far as I can tell there is no way to get Viber to not phone you up every time some stranger on the internet uses your number to register an account.