A method for authenticating a mobile device of a user versus a third-party such that instead of a mobile phone number MSISDN of the mobile device, a Universal Unique User Identifier, U3I, assigned to the mobile device is used, in combination with a secure routing service server constructed to communicate with a third-party server and with an MNO server. The secure routing service server and the MNO server interact to translate the Universal Unique User Identifier, U3I, to the mobile phone number MSISDN so as to enable sending the token to the mobile device.