Respina is one of Iran's larger telecom providers — dedicated internet access, SIP-Trunk, hosted PBX, data center colocation. I joined the Hosted-PBX (Nexfon) team and spent most of my time on two problems: billing and call capacity. I rebuilt the billing pipeline on CGRATES for real-time charging, fixing a long-standing accuracy issue, and rewrote our monthly reporting queries — parallelized with Celery — which cut a 30-minute job down to 40 seconds. On the call-handling side, I refactored our Asterisk-ARI integration into an event-driven Flask microservice, containerized it with Docker, and added multi-processing; concurrent call capacity per instance went from 25 to 130, roughly a 5× drop in infrastructure load. I also set up monitoring with Prometheus, Loki, and Grafana, and worked with the DevOps team on migrating deployments to Kubernetes.