IOS, Android it should work on all platforms including linux, macos, windows atm there is no good XMMP client working everywhere that's why no one use it except GPL folks only.

Whatever we like FOSS or not fact stands we can't convince non geeks to switch if FOSS apps is broken. So far I have not seen any XMMP based apps that works good and easy.

Also people wants media(post links, pictures, sound) not only text messages. This is something telegram has. XMMP may have some half backed approach in some clients.