Inquiries are scrutinising the high profile Optus outage that left some without triple-0 access.

Official probes are focusing on concerns regarding Australians' inability to access emergency services and evaluating the effectiveness of government messaging during the incident.

The outage, attributed to a software upgrade, prompted the resignation of Optus CEO Kelly Bayer Rosmarin. 

Communications Minister Michelle Rowland announced plans after the outage for an inquiry to be led by her department.

The terms of reference for the probe, conducted by former ACMA chief executive Richard Bean, will investigate the technical aspects affecting triple-0 access and explore alternative networks during major outages. 

The findings are expected by the end of February.

A government submission to a Senate hearing on the matter has revealed that two out of three federal communications department staff with Optus mobiles could not dial triple-0 during the outage. 

The review will explore why a reported 228 calls to triple-0 failed to connect.

Regarding compensation for affected customers, the Department outlined existing options, including raising complaints with providers, escalating to the TIO, or pursuing legal avenues. 

Optus says it has been compensating affected customers in cash and account credits.

Optus, initially offering 200GB of data as compensation, faced criticism, leading to the CEO's resignation. 

The government-backed inquiry, separate from the Senate's, will investigate triple-0 access and government messaging. 

Led by Richard Bean, the findings are expected in February, while the Senate's report is due by December 9. 

ACMA has launched its own investigation into the outage too.