Onsite VoIP phone system is where the PBX is a purpose built Open Source phone system which resides on the customer’s site. The main advantage of a VoIP PBX is lower costs resulting in having a business phone system that escapes the traditional cycle of having to replace entire systems for upgrades or expansions, because the traditional manufacturer wants to keep you buying entire new systems or expensive upgrades and propriety phones. Open source solutions allow business to acquire any SIP compliant handsets for use with the system.