How VAPI connects to Asterisk PJSIP for AI voice calls

I run six AI-powered businesses from a single Vultr VPS. Each business needs capabilities. Instead of paying $50+ per month for hosted voice solutions, I built my own system using Asterisk and VAPI. Here's exactly how I connected VAPI to Asterisk PJSIP for AI voice calls. The Problem with SaaS Voice Solutions Most AI voice platforms want you to use their numbers and infrastructure. You pay per minute, per call, per feature. For one business, maybe that works. For six businesses making hundreds of calls monthly, those costs add up fast. I needed control.