Last year Infonetics estimated that the annual ARPU for mobile VoIP user was $13 [here]. 2012, saw a huge decrease.
A new report by Infonetics Research Principle Analysts Diane Myers [pictured] and Stéphane Téral, finds that "While Skype dominates the over-the-top mobile VoIP space, the market is seeing other applications such as Fring, KakaoTalk, Line, Nimbuzz, WeChat and Viber gain in strength. But the fact remains that most OTT mVoIP providers are making very little money per user. In 2012, the average revenue per user was a meager US$7.13 annually. Since this alone is an unsustainable business model, most providers are turning to advertising, third-party apps and wholesale arrangements with traditional operators”
"Infonetics projects the number of VoLTE subscribers to grow at a 145% compound annual growth rate from 2012 to 2017 Combined, over-the-top mobile VoIP and VoLTE services are expected to become a $16 billion business by 2017"
See "Infonetics Research raises VoLTE forecast; Over-the-top mobile VoIP subscribers nearing 1 billion mark" - here.