Post-paid generally is a lot stricter e.g. most telcos want 100 points of ID with at least one primary document such as driver's license or passport [2]. Not sure if that's a legislative requirement though, or just good business practice.
[1] https://www.acma.gov.au/acmas-rules-id-checks-prepaid-mobile...
[2] https://www.telstra.com.au/support/account-payment/id-check-...