They're called 'Travel Alerts' and are only available for Pro subscribers. If you are a Pro subscriber, go here 
https://www.tripit.com/account/edit/section/travel_alerts and set them up.
For the money, it's an excellent investment. It's great in the USA too where flights can change around very quickly (and is often easier than leaving my comfortable seat in the AC/FL to find a monitor).
FYI, here's the options screen:
View attachment 7477
You can select email and SMS for everything except Schedule Changes (that's Email only). It works with AU mobiles, and you can easily change it to an o/s number (you get an SMS with a code to confirm the change). Works great!