Abstract: A method of generating device-specific configuration data during the initial set up of a device (12) comprises, during a configuration process running on the device (12), sending from the device (12) a first message and including a device identifier to a server (40) using a first mode of communication associable with a service identifier, sending from the device (12) a second message including the device identifier to a server (46) using a second mode of communication not associable with said service identifier, processing the first message to associate the device identifier with the service identifier, and processing the second message to query if the device identifier has been previously associated with the service identifier, and if so, sending device-specific configuration data to the device (12) for use during the configuration process, wherein after the configuration process is completed, the device-specific configuration data enables authentication using said service identifier when the device uses sai