Abstract: ? An information transmission system which comprises a system base station including; a transmitter arranged for communication with a plurality of mobile receiver units, via a mobile radio system; a CPU in which data is registered appertaining to a plurality of different subjects; an alert signal generator; and an SMS (Short Message Service) message generator, the alert signal generator being responsive to data stored in the CPU for initiating the generation of an appropriate SMS message by the SMS message generator for transmission via the transmitter and the mobile radio system to a mobile receiver units or units, consequent upon registration in the CPU of data appertaining to a predetermined subject. The system is especially suitable for use in airport passenger flight departure information applications, wherein the mobile receiver units are carried by passengers and used to update them with flight data using the SMS.