Customer complaints to telcos rose in the final months of 2018 with issues over non-NBN fixed broadband services increasing by more than 60 per cent.

Communications watchdog ACMA said 448,470 complaints were received by reporting telco providers during the December quarter, a 12.7 per cent leap on the prior period.

The 30 reporting providers nominated billing and faults as their top two complaints categories, with about half of reporting providers having billing as their top complaint category.

ACMA said the biggest increase in complaints was for non-NBN fixed broadband, with complaints rising 62.3 per cent from 204 to 331 per 10,000 services in operation, despite overall use of the technology declining 5.3 per cent to 2.1 million.

In comparison, complaints over NBN broadband per 10,000 services edged 1.0 per cent lower despite the category having double the number of services in operation with 4.9 million.

The overall median number of days needed to resolve complaints remained steady at six days, while the percentage of complaints referred to the Telecommunications Industry Ombudsman decreased by 9.2 per cent.

Ombudsman Judi Jones urged providers to focus on meeting the needs of customers.

"The publication of internal complaint handling data provides a more comprehensive picture of the consumer experience and supports our work with regulators, government, and providers," Ms Jones said on Wednesday.

Mobile services received the most complaints in the December 2018 quarter with 174,562 overall, but had the lowest proportion of complaints because the category comprises about three quarters of the 41.4 million services in operation in Australia.

Voice-only services over the NBN registered the highest number of complaints per 10,000 services despite having the lowest use.

Faults and connections were the most likely reason for voice-only NBN complaints.