Techniques are provided for establishing a Virtual Desktop Interface (VDI) connection at a virtual desktop thin client (VDTC) device, between a VDI client in the VDTC device and a VDI server in a hosted virtual desktop server (HVDS). A unified communications (UC) control connection is established between a UC protocol stack on the VDTC device and a primary call agent, where the UC control connection is configured to allow the UC protocol stack to register with the primary call agent, and to send or receive commands from the primary call agent that are based on signals from a UC control application running on the HVDS. A UC control backup application is started on the virtual desktop thin client device in a standby mode that is configured to switch to an active mode in response to a failure to establish or maintain the UC control connection, or a failure to establish or maintain the VDI connection. A user interface is launched on the virtual desktop thin client device that is configured to perform UC backup functions.