It’s so strange that out of the box CalDAV and CardDAV support is rare for mobile devices. iPhones are the best somehow, with Android being heavily Google-focused and support is totally absent on non-smart platforms, which is the perfect opposite of what one might expect! It’d make way more sense if the more open platforms were built around open standards, but somehow here we are.

It's "rare" in that Apple, BlackBerry / RIM, and (seemingly, though I never used it) Windows Mobile all supported it.

It was only ever Google that didn't

The fact they now make up half the market is what makes it rare, not that other mobile OS' didn't make it available