Most GSM phones use regular SIM cards. Which are small. The iPhone 4, iPad and uh, not many other devices use next-gen micro SIM cards. Which are smaller. Apple's just proposed a new SIM standard. Which is smallerer.
Reuters reports, via massive telecom Orange's head of devices Anne Bouverot, who says that "Apple has submitted a new requirement to (European telecoms standards body) ETSI for a smaller SIM form factor—smaller than the one that goes in iPhone 4 and iPad." It'll be a real standard, with carriers like Orange backing it. Bouverot says the first devices with the new SIM could show up next year.
So, like iPad 3, iPhone 6. A SIM card doesn't seem like a massive amount of matter to tussle with, but I guess every millimeter counts. [Reuters via Mac Rumors, Image: CC licensed, Thomas van de Weerd/Flickr]