> There isn't really any other way to do it

There is, it's called balancing the probabilities. What's more likely - that someone started a company, developed a full-featured VoIP app, set up all the infrastructure to provide their service, made the app open source and established themselves in the market, all just to secretly harvest people's contact lists.......or are they telling the truth and no data is being uploaded? These are all things Google can verify, they just don't want to.