Australian telecommunications company, Telstra, has advised it will be implementing scam protection measures over and above the Communications Alliance C661: 2020 Reducing Scam Calls Industry Code. These changes are in direct response to the increase in scam call activity across all Australian fixed and mobile phone networks.
Beginning March 1, 2022, users who make calls using an Australian CLI that belongs to Telstra, to another Telstra phone number, will be blocked by Telstra.
You will need to stop making outbound calls with Telstra Caller ID unless the number is housed on Telstra's platform.
All outbound calls using a Telstra number as Caller ID will be blocked from calling Telstra phone numbers; Telstra have advised that the calls will be rejected with a cause code of 21, which should map to a SIP 402 response.