Vodafone remains Australia's most complained-about telco despite big improvements in the past year.
Between July and September, the industry ombudsman received 12.2 complaints for every 10,000 Vodafone services.
That's close to double the 6.8 recorded for second-placed Telstra. The number for Optus was 4.6.
The figures for the quarter are the first to cross-reference complaints with customer numbers.
"We don't minimise the seriousness of these numbers," said Matt Paterson, Vodafone's head of customer care.
But he said the company was heartened by a significant drop in overall complaints, which fell 30 per cent in the past year to reach 6,267 in the September quarter.
Mr Paterson pointed to recent measures to reduce bill shock and cut down on roaming and excess data charges.
The ombudsman reported on Wednesday it fielded 30,539 phone and internet complaints in the September quarter.
That is down about 5000 on the same period in 2013 and the least in any quarter since September 2007.
The comparative data, however, was only available for five companies that volunteered data.
Internet service provider TPG, for example, was not included despite being the fourth most complained-about company.
COMPLAINTS PER 10,000 SERVICES
* Vodafone: 12.2
* Telstra: 6.8
* Optus: 4.6
* iiNet: 5.7
* Amaysim: 1.4
