Hahaha! 
Thanks for making my day, Charlie!
Perhaps someone who can read Japanese could translate the backs of the image posted by @linkdu83 ? Not sure if that gives any useful information.
Btw Charlie, those Mini Cards are still pretty big compared to the miniature 'ultra-kawaii-cutey’ 
Japanese Pokémon Mobile Phone Charm Promos (thanks to @charchu I currently have the Pikachu incoming):
Greetz,
Quuador