I need a SIP professional to link my existing vapi.ai number with my on-premise Grandstream PBX and leave me with a fully registered trunk that can place and receive calls without hiccups. Both platforms are already active, so the job focuses purely on configuration rather than account creation. Here’s the brief: • Implement two trunks—one that registers via static IP and another that authenticates with username / password—so I can switch methods on demand. • Complete the setup remotely on the Grandstream interface and in the vapi.ai console, then run live test calls to confirm two-way audio. • Provide a short note of any parameters you touch (SIP server, NAT, codecs, authentication strings, firewall rules) so I can replicate or edit the settings later. The job is finished when the trunks show “Registered” on both ends, inbound and outbound calls work, and the quick configuration summary is in my inbox. Grandstream UCM access and vapi.ai portal credentials will be supplied as soon as we kick off.