How does it get your information from the calendar? ...I use Apple's calendar on my iPhone
iPhone calendar setup is a cinch. Pair your iPhone with MS as normal. Turn on remote access Settings / Safety & Security / Remote Access / ON so the Tesla App can reach your MS. From the Tesla App, enable Calendar in it's Settings, and when prompted by iOS on your phone, BE SURE you allow calendar access for the App (or go to Settings and make sure). Then back at your MS, Settings / Apps / Calendar / whichever-option-you-want (I use "Show Calendar Upon Entry"). Page 119 of the current Owner's Manual has more detail.
By default, all events on your iPhone's Apple Calendar will appear on your MS calendar, which includes personal calendars you maintain discretely on your device, iCloud, Birthdays and even subscribed calendars you may have like US Holidays.
Fill in the event name, start time, and optionally a location (which is a GREAT way to get addresses easily entered into your MS Nav with a single touch), perhaps some event notes, and events for the next two days will come across to your MS. If there is a phone number somewhere in the text, you get a button so with a simple touch it dials. If you don't want to show some of your calendars in MS, touch the icon in the upper right of the MS calendar pop-up and you can limit them there.
I do not use calendars like Google, so cannot comment upon how those do or don't work with iPhone, but suspect if you have a Google or Yahoo! Calendar also connected as part of your Apple Calendar, the same basic info will also come across. I wouldn't see why not.
Calendar works well for me even in this beta version, and has been flawless since MS introduced Calendar a few months ago. It's proven to be a good set of workarounds to get things like Nav addresses into my MS from my Mac/iPhone/iPad without my needing to rekey into Nav while seated.