I've added it via native support, unfortunately I can't share the code as its under contract with a customer but its not too difficult to do, I have it running in iPhone and Android and compiling in Windows Phone (but untested as of today).
For each platform implementation I pretty much just googled it and found the code needed and made minor adaptations to make them consistent on all the platforms.
The only minor gotachas are Windows Phone uses a different epoch and time measure measurement than the other two and all platforms have slightly different options for the event status (Busy, Available etc.,) but mostly its straightforward and works.
Good luck.