There are a few VoIP softphones that work with SIP for smartphones that do well. Zoiper is one of them. The most important thing is that it is free. It does have a premium version with additional features, but it is quite cheap. For non-geek readers, note that Zoiper is not a VoIP app with a service like the Skype type. It is a softphone with which you have to use a SIP provider of your choosing. Register with a SIP provider and obtain a SIP address, configure your Zoiper client then use.


Configuration is not very much straightforward, so you need to go through settings for quite some time. Zoiper is quite rich in features and settings, which while making it interesting, also makes it tedious to set up. You could as well make mistakes and run the risk of failing to make things work, but if you are assisted things should go smoothly. The interface is impressive in the sense that it is loaded with features and configurations.

Fortunately, Zoiper offers a side product that helps you automatically configure your VoIP, with auto configuration and auto provisioning. There is a free version which is basic, and two other schemes with are paid and more customizable. 

Zoiper free lacks certain elements that come only with the gold premium product, like video support, call transfer and high definition audio. The free features make it an interesting tool. It supports Bluetooth, 3G and WiFi; multitasking; a list of codecs; built-in echo cancellation among others. 

Download link on Google Play for Android devices and on App Store for iOS.