Optus ended the December quarter around 8.9 million mobile subscribers, according to parent company SingTel (ASX:SGT).
Optus recorded net additions of around 88,000 customers during the quarter. The operator's postpaid customer base hit 4.6 million, up 14% from a year ago.
But prepaid customers declined by 62,000 over the same period, with additions impacted by a higher than average churn rate.
SingTel said Optus now covers 97% of Australia's population. Over half - some 4.84 million – of Optus' customers are on the operator's 3G network.
SingTel also saw its highest postpaid net adds in two years for its domestic Singapore operations, with total net adds of just over 100,000.
Growth from SingTel's regional affiliates, including India's Bharti Airtel, helped the company grow its groupwide customer base to 383 million by the end of the year.
SGT shares fell 1.24% during Wednesday's trading to close at $2.380.