A method and system for providing a fallback solution in a multi-tenant communication system is provided. A cloud-based call processing service receives a voice call initiation request from a first mobile device located at a first communication system. The voice call initiation request includes a request to complete a voice call with a second mobile device located at a second communication system. Resources are allocated at the first communication system and the second communication system. The cloud-based call processing service establishes a call between the first mobile device and the second mobile device. At some point the first communication system determines that it should fallback to single site operation. In fallback mode, call processing functionality is performed at the first communication system for the first mobile device.