When you sign up for a Belong nbn plan you’ll receive the standard inclusion of Dynamic IP. Check out more info on What type of IP address do I need? 

Dynamic IP address 
If you have a Belong ADSL service and switch to Belong nbn at the same address, you’ll be provided with a Dynamic IP address, even if you currently have a static IP address. This is due to the removal of Static IP addresses at Belong. 

Some Belong customers have previously purchased a Static IP address which they can continue to use. However for new customers, and those moving homes, you will no longer be able to purchase the Static IP address. 

Note: If you’re currently on a Static IP and move to a new home or remove it temporarily, you won’t be able to return to static. Instead, a default Dynamic IP will be issued to you.