cheap VoIP recommendations ? anyone ?

I'm looking for the cheapest VoIP service for south Africa/johannesburg (i need coverage for this area) also how do I set it up on my HTC EVO 3D(it uses Android BTW) is there an app I download ? and which app do you recommend ? thanks in advance ; note I have never done something like this before. also does (encrypted spelling again) the person I'm phoning need to have VoIP activated on their device or need to download any apps ? can I phone anyone without VoIP in other words ?

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