For use in a switch comprising N call application nodes (CANs), a method of upgrading call process server applications that comprise a primary call process and a backup call process executed on different CANs. The method comprises the steps of: 1) receiving a shutdown command to shutdown a first call process server application comprising a first primary call process executed on a first CAN and a first backup call process executed on a second CAN; 2) disabling the first primary call process such that no future call traffic associated with the first call process server application is directed to the first primary call process; 3) re-designating the first backup call process as the new primary call process of the first call process server application such that all future call traffic associated with pre-existing calls handled by the first call process server application is directed to the re-designated first backup call process; 4) moving a second backup call process, if any, associated with a second call process server application and resident on the first CAN to a different CAN; and 5) installing an upgraded first call process server application on the first CAN, such that an upgraded first primary call process of the upgraded first call process server application executes on the first CAN and creates on the first CAN an upgraded first backup call process.