I was introduced to Viber the other day - a neat and very elegant alternative to some parts of Skype, Google Talk etc, run on Amazon servers, that uses your real cellphone number to make and receive free calls and messages to and from other Viber users (Android and iPhone only, Blackberry client will follow). Incredibly easy to use: just install and go, that's it, no registration, no noticable setup. It gives excellent sound quality (even over 3G), no ads, uses your existing address book, has a really clear and apparently very ethical privacy policy (except that it is in the US, so suffers the usual serious concerns about US government agencies being able to access data). If the person you are calling/texting is not on Viber, it just falls back on your normal cellular provider to dial the number. It even passes through most firewalls. Seems pretty faultless, as far as I can tell.

Apart from the issue of privacy in the US, I only have one puzzling concern: with no ads, no hidden connection charges, no premium services, no selling of personal data, strong controls preventing release of personal data to anyone at all, indeed no obvious means of revenue generation and some big infrastructure costs, how on earth will they make their money?