Optus has confirmed that services have returned to normal following a network issue affecting text messages being sent between Telstra and Optus customers, with some messages being delayed and others failing to send altogether.
The telco is now processing any messages that were delayed or undelivered during the outage.
"SMS and MMS messages between Optus and Telstra customers are delayed and/or intermittently failing," an Optus spokesperson said earlier today.
"Optus technicians have identified the cause of the issue. The issue does not affect voice calls or data, or SMS and MMS to Vodafone customers.
Financial services company ING Direct had warned that due to the Optus outage, some customers have not received banking messages.
"Due to an Optus outage, customers on the network may experience significant delays in receiving SMS from ING Direct," the company said in a tweet.
Optus' mobile network covers 98.5 percent of the Australian population and 15.6 percent of the nation's landmass, according to the Productivity Commission's draft report into the telecommunications universal service obligation (USO) published in December, while Telstra's mobile network covers 99.3 percent of the population and more than 31 percent of the landmass.
Between them, Optus and Telstra hold 62.2 percent of total mobile market share in Australia -- 39.9 percent by Telstra and 22.3 percent by Optus.
Optus' SMS and MMS issue follows rival mobile telecommunications provider Vodafone Australia's voice outage earlier this week, which saw some customers lose voice services for a period of four hours.
Vodafone attributed the issue to a fault during scheduled work.
"The issue, which was caused by a fault during scheduled work on the network, resulted in voice traffic congestion from 10.30am AEDT. The issue was fully resolved by 2.30pm AEDT," a Vodafone spokesperson said on Wednesday.
Vodafone suffered another voice outage lasting around three hours back in January, which was caused by an error during planned work on the network, and a seven-hour 4G mobile outage affecting data, voice, and text messages in September last year, which was caused by a router issue.
Updated at 3.30pm AEDT, March 17, 2017: Optus has repaired the issue.