Libon is a free iOS app that allows users to call for free landlines and mobile numbers in a number of countries. According to Libon, the service offers free calls with HD sound, an audio quality that is not offered by competitive applications on mobile.
Only international Voip out calls are available, calls to local numbers are not possible, however, you can call other local Libon users, they need to download the client from the appstore. I did not try Libon yet, so I cannot confirm the quality of the service.
In addition to free international calls, Libon offers a smart visual voicemail feature: you can customize your greeting message according to each caller. With the free app, you get the regular voicemail and the visual voicemail with speech to text transcription is available in Libon Premium. The Premium costs £1.99 in the UK, €2.69 in Europe, and $2.99 in the US.
Libon is available in the 80 Apple appstores around the world and free international out calls are available in the following countries: Canada, China, Hong Kong, Puerto Rico, Singapore, Thailand, USA, Austria, Belgium, Croatia, Czech Republic, Denmark, Estonia, France, Germany, Greece, Hungary, Ireland, Italy, Luxembourg, Netherlands, Norway, Poland, Portugal, Russia, Slovakia, Spain, Sweden, Switzerland, UK.
The Android beta will be launched in a few weeks. Check the video demo here.