Asterisk SIP Trunk Configuration on Linux

I need a reliable SIP trunking solution running on Asterisk under Linux. At the moment I’m unsure whether the server already in place can be salvaged or if it will be cleaner to start from scratch, so the first step will be a quick audit of what’s there... (Budget: ₹750 - ₹1250 INR, Jobs: Asterisk PBX, Debian, Documentation, Linux, Security, SIP, Telecommunications Engineering, VoIP)