VoIP Services (Domestic VoIP Calls and International Long Distance VoIP Calls) Market by Configuration (Phone-to-Phone, Computer-to-Phone and Computer-to-Computer) for Hosted Business, IP Connectivity, Managed IP PBX, Individual Consumers and Corporate Consumers: Global Industry Perspective, Comprehensive Analysis, Size, Share, Growth, Segment, Trends and Forecast, 2015 - 2021