Optus customers were unable to pay bills for up to four hours yesterday after the telco's billing system crashed.
The outage affected Optus phone (Interactive Voice Response), online and Optuspay credit card payment systems yesterday morning.
An Optus spokesperson said the problem was caused by an "isolated software issue" which affected credit card payments.
Customers were able to make payments via BPAY, at Australia Post offices and at retail outlets.
The service was restored "late yesterday afternoon", according to the spokesperson.
The telco did not elaborate on the reasons for the crash.
