PJSIP in Asterisk provides a wide range of features and capabilities for handling SIP communications. Here are some cool things you can do with PJSIP: 1. **Advanced Call Routing:**    PJSIP allows you to create sophisticated dialplans for call routing. You can implement conditional routing based on time of day, caller ID, dialed number patterns, and more. 2. **WebRTC Support:**    PJSIP has built-in support for WebRTC, which enables real-time communication directly in web browsers. This can be useful for building web-based applications that involve audio and video communication. 3. **Endpoint Groups:**    You can organize your PJSIP endpoints into groups, making it easier to manage and apply configurations across multiple endpoints simultaneously. 4. **TLS and SRTP for Secure Communications:**    PJSIP supports Transport Layer Security (TLS) for secure SIP signaling and Secure Real-time Transport Protocol (SRTP) for securing the media stream. This is crucial for ensuring the privacy and integrity of communications. 5. **Custom SIP Headers:**    Customize SIP headers for specific scenarios. This allows you to add, modify, or remove headers based on your requirements. 6. **Real-time Monitoring and Logging:**    Use PJSIP's monitoring features to capture and log SIP traffic in real-time. This can be valuable for debugging, troubleshooting, and analyzing SIP messages during call processing. 7. **Integration with External Services:**    Integrate PJSIP with external services, such as VoIP providers, gateways, or other telephony services. This allows you to extend the capabilities of Asterisk and leverage external resources. 8. **Voicemail and Messaging:**    PJSIP can be used to implement voicemail systems, including custom greetings, message storage, and retrieval. You can also integrate voicemail with email or other messaging systems. 9. **Conference Bridging:**    Set up conference bridges to allow multiple participants to join a single call. PJSIP supports the creation and management of conference calls. 10. **Dynamic Configuration:**     PJSIP supports dynamic configuration, allowing you to make changes to endpoint configurations without the need to reload the Asterisk configuration. This is particularly useful for making real-time adjustments. 11. **Call Recording:**     Besides `MixMonitor`, you can explore other call recording options, such as `Monitor` or using external recording applications. This is useful for compliance, quality assurance, and training purposes. 12. **Interoperability with Other Protocols:**     Asterisk, with PJSIP, can support various protocols beyond SIP, including IAX (Inter-Asterisk eXchange) for interconnecting Asterisk servers. These are just a few examples of what you can do with PJSIP in Asterisk. The flexibility of Asterisk allows you to create custom telephony solutions tailored to your specific needs. Always refer to the official Asterisk documentation for the most up-to-date and comprehensive information.