The following review written by one of the Software Informer contributors applies to version 4.3
Rynga is a free Voice-over-Internet-protocol software tool from Betamax. It will allow you to call abroad for very little money (or even free), as you can configure it to use broadband as well as toll-free numbers from your mobile.
Setting up Rynga is straightforward and simple.
In order to make calls you need first to buy credits from Rynga (just like any regular mobile top-up), which you can obtain online. It supports various payment methods such as VISA, PayPal, CashU, and others. By purchasing these credits, depending on the plan you signed up to, you will be allowed to make calls for a fixed period of days. In the Info tab, you will have real-time details regarding your balance.
You can make PC-to-PC calls, send SMS messages to your contacts, and even make free wi-fi calls using your iPhone (other mobile phones, including Nokia, Android, and Windows Mobile are claimed to be supported soon.) A signal in the bottom-left corner will show you graphically the quality of the call - this may differ according to your Internet connection and its load (active downloads and uploads).
Rynga provides easy ways to import your contacts from MSN, Skype, and Outlook.