Setup Linux Telecom Server

I need a seasoned telecom engineer to turn a fresh Linux box into a full-featured communications platform. The build must rely exclusively on open-source components and cover every real-time channel we use—VoIP, PSTN, instant messaging with presence, video calling and broader multimedia handling... (Budget: $30 - $250 USD, Jobs: Asterisk PBX, Debian, Linux, SIP, System Administration, Telecommunications Engineering, VoIP, XMPP)