Step 5: The Autodialling Business Card!
This is all possible because of miniature programmable microcontrollers - they are now so small and so cheap, they can be put into disposable items. The one I use is made by "Microchip", and costs 39 cents in quantity (and not much more in singles). It can run any small program that you write, and can run it at 4 million instructions per second. I can safely claim (for the moment), that I have the world's most sophisticated business card! You could easily program the microcontroller to do any number of things that fit within the program memory instead - perhaps a simple version of the "business card torch" described earlier that has a flashing light or even "S.O.S." function. Your imagination is the limit here.
A bit of a warning first, though - this is well and truly in the class of an experimental device - it needs considerable tweaking to get working on an individual phone system, and doesn't work on mobiles. It may also not work on some PABX (business phone) systems, depending on the brand. I have quite a bit of experience in electronics, and some good test equipment at my disposal, and this design isn't really setup to be able to use reliably on all phones, so only "extreme experimenters" and those willing to improve the technical aspects of this design should attempt construction - this is definitely not a beginners project, but as mentioned, it might inspire some other designs, rather than being ultimately a really useful one by itself.