The 'intelligent' stamp is a claimed world first, incorporated in Royal Mail's latest Great British Railways edition. The way it works is very simple.
You need an app called Junaio, an augmented reality browser that is already available in the iTunes store and Android market for free. Once you've opened it, go to the Royal Mail channel, select the Great British Railways logo, and open up the smart phone camera.
If you receive an envelope with the special edition stamp on it, you simply point the phone camera at it. This launches an online video of the legendary actor Bernard Cribbins reading WH Auden's poem 'The Night Mail'.
You might have seen him most recently in the David Tennant-era Doctor Who playing Wilfred Mott, one of the Doctor's companions. Older readers could also recognise him as the voice of The Wombles, inspiration for baldy band Right Said Fred and star 1970s kid's classic The Railway Children.
Royal Mail Stamps spokesperson Philip Parker said, "Royal Mail's special stamps mark key events and anniversaries in the UK's heritage through a programme which aims to be both educational and informative."
"Through Intelligent Stamp technology, our stamps will open up to a whole new world of information, interest and fun to collectors and the millions of people who will receive them on letters in the coming months alike."
Nice words, but we're not sure about how augmented reality technology is going to help our usual concerns about the Royal Mail. Things like how quickly our letters arrive.
Would you like to see this on all stamps? Is it a gimmick, or something you're excited about?