Allow configuration and inclusion of custom SIP headers when routing calls from Thread Voice Agents to external contact centers (e.g., Webex Contact Center). This would enable passing specific parameters (such as contact info, call reason, and categorization) seamlessly during call handoff. Ideally, this feature should support bidirectional integration, so external contact centers can also pass calls into Thread Voice Agents with SIP headers for targeted automation tasks. This would greatly enhance integration flexibility and automation for organizations using hybrid AI and traditional contact center workflows.