Daring Fireball: Viber

Under the bad he lists:

    When you sign up for Viber, they send
    a push notification to everyone in your
    address book who has already signed up for
    Viber. I’m not sure it’s right to call this a
    privacy issue, per se, because it’s only sending
    notifications to people whose phone number you
    have and who have your phone number, but I’m
    opposed to any service that sends notifications
    to others on my behalf without my consent. And
    there is no way to turn this feature off.

I'd say it is a privacy issue per se, because it is NOT true that everyone whose number I have in my address book has my number. There are people in my address book who I am careful to only call from my office phone, specifically because I do not want them to have my iPhone number. I also have numbers of people who I have never called from any phone, and who do not have my number. I have them there for certain emergencies.