For the pass few weeks, a few of my friends asking me that did I installed Viber.
Viber is a free iPhone application, to make free call from Viber to Viber. It will works on iPod Touch with newer OS version (iOS 4), but it was not officially supported, stated in Viber FAQ.
Viber is just like Skype and FaceTime. You can call your friends for free, through Wifi or 3G connection. More precisely you can refer Viber as a voice version of Whatsapp. Viber is on the top list of iTunes app.
Whatsapp is a paid application on iPhone, it has an Android and BlackBerry version too. User need to purchase the application (cost USD0.99 on iPhone now), but once installed it can send SMS to another Whatsapp application for free.
Whatsapp will scan your contact list on your iPhone (or iPod Touch), notify you those who have installed Whatsapp which is on your contact list. Viber do the same thing, it scans your contact list (identified by phone numbers), and tell you who has Viber.
There are good and bad about grabbing the contact list. The good thing is easy setup. Is zero setup like FaceTime, user don't have to add in their friends one by one.
The bad thing is about privacy. The application might assume that all the contact on my list are my friends, which is not true. Some of them are business partners, some could be my competitors, some could be just a strangers that I meet yesterday night.
Without approval and blocking features, others could spam me (with Viber, Whatsapp or similar application), which might cause security issues as well.
Personally I prefer Skype. These days, less people using Skype for communication. When I launch Skype, only 2 contacts appear online out of my 20 Skype contacts.
People prefer Viber, may be it is a trend now. Zero configuration (or dead simple) is a most wanted feature for most users who doesn't know how to configure or lazy to do so.
Viber software is still new, the stability of the software need to be improved, more functions like SMS will be available soon. More platform like Android and BlackBerry will be supported in the future.
Why Viber (and Whatsapp)? It still be a big question mark with me.
I install the Viber simply because my friend need to call me through Viber and ask me to do so. If Skype don't improve themselves, they will be taken over by new comers.