This document discusses open source telephony (OST) and proprietary solutions. It provides an overview of OST standards like SIP and Asterisk elements. It describes the fragmented OST market in 2007-2008 and how proprietary solutions can add value by providing enhanced features to softphones, call management, contact management, and presence. Examples are given of OST usage in IP PBX systems, mobility extensions, multi-site scenarios, and VOIP trunking. The benefits of solutions that combine OST and proprietary elements are outlined, such as reduced need for expertise and improved support.