Optus is again the most complained about telco, having received 5.9 complaints per 10,000 services in operation (SIO) for the October to December quarter -- a year-on-year rise of 9.3 percent, though an 11.9 percent decrease from the previous quarter.
The statistics, reported in the Telecommunications Industry Ombudsman (TIO)'s Telecommunications Complaints in Context report [PDF] for the last quarter of 2015, saw an overall 28.4 percent decrease year on year in consumer complaints about telcos, from 6.7 down to 4.8.
Vodafone Australia is continuing to see the biggest drop-off in complaints, with a 66.7 percent drop year on year, from 10.5 complaints per 10,000 SIO down to just 3.5.
"It's very pleasing to see Vodafone's ratio of complaints drop even further in the December quarter, with today's result representing an 82 percent decline in less than two years," said Vodafone director of Customer Service Errol van Graan.
"We've worked very hard to make improvements across the business to offer our customers a first-class network, outstanding customer service, and worry-free products."
Telstra also kept falling, from 6.4 down to 4.9 -- a 23.4 percent decrease year on year, and a 10.9 percent decrease quarter on quarter.
Mobile services operator Amaysim, which last month acquired mobile virtual network operator Vaya for AU$70 million, saw a 53.3 percent decrease in complaints year on year, from 1.5 per 10,000 SIO down to 0.7.
In November, market research company Kantar revealed that the rise of MVNOs in the no-contract market has led to incumbent telco Telstra falling overall in market share due to a drop in its post-paid customers.
"Cheaper calls, followed by better customer service, are cited as the key reasons for changing networks ... noteworthy beneficiaries of the Telstra churners are Amaysim, TPG, and iiNet," Kantar said.
Amaysim came in fifth place for the overall mobile market share, at 3.8 percent, up 0.1 of a percentage point year on year behind Telstra, Optus, Vodafone Australia, and Virgin. Other MVNOs accounted for 9.7 percent of the total market, a rise of 2 percent year on year.
In the no-contract market segment, Amaysim gained 1.4 percentage points, to account for 8.7 percent of the market, and in the post-paid sector, Amaysim stayed fairly level, losing 0.1 percentage points to retain 1.4 percent of market share. For the prepaid market, Amaysim dropped to 5.8 percent.
Kantar in April similarly recorded a jump in the no-contract market, up 2.1 percent quarter on quarter to 9.5 percent of the total market.
"Australian consumers are becoming increasingly exposed to the benefits of SIM-only tariffs, which offer 4G connections, rollover data, no lock-ins, and a generous amount of data, to name a few, for a comparatively low cost," Kantar said at the time.
The MVNO sector is continuing to grow, with Kogan Mobile relaunching in October on the Vodafone network.
In December, the TIO revealed that overall complaints were at their lowest for nine years, numbering 26,023 during the quarter -- a 14.8 percent decrease from the 30,539 complaints recorded during the same period in 2014.
Issues with mobile services made up 40 percent of all complaints, while complaints about internet services contributed to 32 percent, and landline issues made up the remaining 28 percent of all complaints.
Billing and payments accounted for the highest proportion of all complaints, at 44.3 percent, followed by customer service, at 39.8 percent; faults, at 30.4 percent; complaints handling, at 26.9 percent; contracts, at 23.9 percent; credit management, at 17 percent; connections, at 12.1 percent; and other issues, at 5.9 percent.
Mobile complaints fell to 10,340, a substantial drop of 31.2 percent year on year from the 15,034 recorded over July to September 2014. Complaints about excess data charges also decreased, down 50.3 percent from 2,524 in the same quarter in 2014 to 1,254 in 2015 -- the lowest number in almost six years.
There were 46 telecommunications service providers with more than 25 complaints during the quarter, including Telstra, Optus, Vodafone, Vaya, NBN, and Amaysim.
NBN complaints grew by 4.6 percent quarter on quarter to reach 2,262 during July to September 2015.