The three biggest telcos have spend and usage tools to help you know how much of the different types of services you are using.
Tools to monitor calls and data usage are available on the Telstra website by selecting 'My Account' from the Telstra home page. There is also an app available for use on portable devices.
Optus provides several options for customers to track their usage and keep their costs down, such as Optus My Account (online usage meter), My Optus App (via mobile handsets), SMS and email alerts, and prepaid mobile customers can check their usage by calling/texting 1509 from their Optus handset (freecall).
There are several pages on the Optus website that provide advice on this such as:
Post-paid plans: these options are available 24/7 and are free to use in Australia.
Pre-paid: these options are available 24/7 and are free to use in Australia.