1. A cable television video messaging system for selectively inserting a desired input message into respective program signals output on multiple channels of a cable television system, said cable television system having a headend facility where multiple external program signals are channelized by means of individual channel modulators having program signal input means and are exported to a cable network for transmission to a viewing audience, said video messaging system comprising: a) a remotely activatable input message decoder to receive, from multiple sources, incoming message information regarding a video message to be displayed on at least one channel, said message decoder decoding message descriptors embedded in or accompanying said incoming messages; b) an intelligent message-management device for routing messages to at least one designated channel according to said message information and in accordance with system-based instructions; and c) a video injector to combine said video message with a baseband program video signal for said designated channel to produce a channelized messaged program video signal; wherein said channelized messaged program video signal is supplied to said channel modulator program input.