Techniques are provided for establishing a Unified Communications (UC) session between a client endpoint device and remote endpoint devices, the client endpoint device managing the session using a first-party call control protocol in response to commands from a third-party control protocol and user input. A hosted virtual desktop (HVD) generates an HVD image and communicates it to the client endpoint device for display, via a virtual desktop interface (VDI) protocol. The HVD image comprises a UC user interface generated by a UC application on the HVD, the user interface comprising at least one user interface element and at least one placeholder where a client-provided user interface element may be inserted. A client UC application receives the HVD image and inserts client-provided user interface elements over the placeholders before sending the integrated image to a client operating system to be rendered on the display of client endpoint device.