Thanks for your comments and questions.
Viber has 3 main advantages:
1. Viber's interface is very easy to use - it looks completely similar to the iPhone basic application, and this makes a huge difference for most users in the world. Simple elegance is what works.
2. Viber does not require login/password in order to log in, unlike the great majority of VoIP applications today, but instead it uses the user's original cellular phone number. This makes the registration process very quick, and helps users find other friends who have Viber very easily. This way more and more friends recommend each other to install Viber, and have free calls and texts.
3. Finally, Viber doesn't have to be open when receiving a call, thanks to Viber's support of Push Notifications feature. This means that Viber saves battery, and that users are always available to receive Viber's free calls.
Lastly - we believe that the service itself that Viber provides, in terms of call quality, functionality, etc., is a very reliable one, and users appreciate that and choose to install and use it on a daily basis all around the world (it's popular both domestic and international).
Sure, Viber still doesn't contain all the feature we'd like to see, but you have to remember that the app is still very young. It's constantly improving, and we guarantee you that with each and every version, new features (big or small) will be added.
Patience is needed