But the real culprit: . Many routers try to help VoIP calls by modifying SIP packets, but Pepephone’s default firmware had a buggy implementation. They turned it off in the router’s “Advanced → Firewall” settings.
: If the standard IPs don't work, you can find your specific gateway by opening a Command Prompt (Windows) and typing ipconfig , then looking for the Default Gateway entry. ip router pepephone