Virgin Mobile customers have lost service for the second time in two weeks after another network failure on Thursday morning.
Many users were unable to call out due to what the telco said was a service disruption.
Earlier this month, a partial network collapse left almost 450,000 post-paid Virgin customers unable to make calls, send texts or use data.
A company spokeswoman said Thursday's outage affected a smaller number of people, and could have been fewer than 100 nationally.
"A small number of customers experienced difficulty making national calls for a short period of time this morning ... we quickly resolved this issue and apologise to our customers for the brief disruption to their mornings."
The spokeswoman said data and text-messaging services had not been affected. She said the two-hour outage was not caused by the same problem that was behind the May 3 network crash, when a system fault incorrectly recognised post-paid mobile services as pre-paid services with $0 credit.
Virgin customers turned to social media on Thursday to vent their frustration.
"Second outage in two weeks ... getting ridiculous," posted Danielle Bunyan, of Perth.
"Once again I am unable to make calls because 'my balance is too low' ... I am on a post-paid [plan] and all my bills have been paid. So what's going on?"
Vivian Matti also said she was experiencing the same problem as two weeks ago.
"It keeps telling my balance is too low, however, I am on post-.paid ... this is really unacceptable," she said.