This document discusses integrating Open Source Telephony (OST) systems like Asterisk with the proprietary Skype system. It describes SkypeGateways like Skip2PBX that allow interoperability between the two systems. Skip2PBX translates Skype's VoIP protocol into standard SIP that is compatible with OST systems. This allows a company to integrate Skype services like low-cost calling and presence into their PBX and manage calling from Skype clients like phones and laptops as internal extensions.