Vodafone and Optus customers across the country are unable to make or take phone calls or send text messages and use data due to widespread outages at both networks.
The issue is also affecting customers on telcos who use Optus' network, such as Amaysim andVirgin Mobile.
In a statement Vodafone said the outage on its network had been caused by a failed transmission link and that engineers were working hard to restore coverage.
Some Vodafone customers are unable to make or receive phone calls while others are experiencing poor quality, a spokeswoman for the telco said.
It is unknown exactly how many people have been affected but there are reports of disruption in all states.
The Vodafone spokeswoman said the outage was "intermittently" affecting customers but could not say when it would be fixed.
"We're aware that we do have a network outage. We're just trying to understand where it is exactly," she said.
It's understood the Vodafone network first failed in Western Australia this morning. The spokeswoman said customers on the east coast started to experience problems about 12.40pm.
Shortly before 3pm, Optus said it was also experiencing network outages.
A spokeswoman said it was unclear what had caused the outage.
Optus has since posted on its Twitter account: "UPDATE Those customers affected, please turn your phone off & then on. This should fix the problem. We apologise again for the inconvenience."
Hundreds of frustrated users have taken to social media to express their annoyance.
Vodafone's Twitter help page responded to users by telling them the company was working hard to "get it fixed up ASAP so sit tight".
Mother of two children Fran Rimrod said she was at home with a sick baby when she discovered her Vodafone mobile was not working.
"To just lose your service without being told - that's appalling. People rely on that," Ms Rimrod said.
"My other daughter's on the way to hospital with my partner and it would have been nice to call them to see how they are going."
Ms Rimrod tried to contact Vodafone and was frustrated when she did not receive a response.
"What's the problem with sending people an email or a message on Twitter or Facebook? We live in an information age, there are ways to tell people," she said.
Have you had problems with Vodafone this morning?