Enable Built-in-Bridge for all phones (optional)

Built-in-Bridge setting can be enabled on per-phone basis or on system level (default to all phones).

Access the System > Service Parameters menu option in Cisco Unified Communications Manager Administration, select your CUCM server from the Server list and Cisco CallManager from the Service list:

Service Parameter Configuration

To enable Built-in-Bridge on system level change the option Clusterwide Parameters (Device - Phone) -> Builtin Bridge Enable to On:

Clusterwide Builtin Bridge Enable