I've used International Reply Coupons as a ham. When hams 'work' each other they exchange something called QSL cards that are the size of a post card confirming the conversation. Speak with enough US States or foreign countries you can submit your QSL cards to qualify for awards like Worked All States (WAS) or countries confirmed (DXCC).<p>When working overseas hams, particularly when they live in the third world it was common to mail them enough IRC's to cover the return postage for them. Now while QSL cards haven't disappeared most of it has moved to the web and digital confirmations.
I sent these out with my international wedding invitations (in Japan it's normal to include a stamped reply postcard). Had to go around several large post offices to get enough (indeed I thought they must've stopped making them and only be selling leftover stock, although the wikipedia page and Japan Post website suggest otherwise).<p>Felt like a fun old-timey experience, like sending a telegram or postal order. Most of my relatives apparently couldn't work them out though, even though I included detailed instructions.
I used them to write to a short wave radio station, so they send a QSL card. <a href="https://en.wikipedia.org/wiki/QSL_card" rel="nofollow">https://en.wikipedia.org/wiki/QSL_card</a>
Is it possible for consumers to still buy these from overseas? My country seems to have stopped selling them, but I'd love to mail one to a faraway friend.