A call processing system includes a call processing server. The call processing server processes calls for an internal network that employs SIP features and functions. The call processing server can receive calls from or send calls to one or more external communication endpoints that are not part of the internal network. However, the call processing server can associate a floating user agent with the communication from the external communication endpoint and lock the floating user agent to a gateway. After locking onto a gateway and initiating the call, the floating user agent can then publish call event status and receive SIP primitives similar to other SIP-enabled devices.