Complaints about Optus have increased 47 per cent, while complaints about Telstra have dropped 21 per cent in 2011-12, according to the Telecommunications Industry Ombudsman (TIO).
Optus complaints have been driven by mobile-related services, according to the TIO, such as faults, inadequate spend controls and disputed internet charges.
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Complaints about Vodafone also increased 11 per cent, with complaints primarily about inadequate spend controls on mobile phones and internet usage charges on mobiles.
Meanwhile, complaints about Virgin also increased by 33.1 per cent and complaints about TPG dropped 23.7 per cent.
Overall, consumer complaints about telcos dropped 2 per cent in the 2011-12 year to 193,702.
"There has been a clear trend, since April 2012, of reduced complaints, with the last quarter of 2011-12 being our quietest for almost two years," Simon Cohen, ombudsman at the TIO, said in a statement.
"This is a positive sign that reflects the focus by a number of telcos on improving their customer service."
Two out of three complaints were about mobile phones, with an increase of 9.3 per cent in 2011-12. Complaints included poor coverage, billing disputes and a lack of clear information to consumers at the point-of-sale.
Complaints about financial over-commitment due to inadequate spend management tools to track usage doubled to 15,752; data roaming disputes increased 69 per cent to 4186; and total billing charges increased 33 per cent to 13,943.
"Complaints about unexpectedly high bills and unnecessary financial over-commitment point to the urgent need for strong spend management rules, including those that are included in the new Telecommunications Consumer Protection Code," Cohen said.
"While these rules do not apply until 2013, or in certain cases 2014, it is a positive sign that some service providers have already taken steps to introduce better consumer notifications about high usage."
Cohen also told a press conference the TIO has begun to receive some complaints about the NBN.
"We don't specifically report on complaints about infrastructure providers such as the NBN, but we have had a very small number of complaints about consumers who have been on NBN services," he said.
Overall, the largest number of complaints were recorded in NSW, with 60,398 complaints, followed by Victoria, with 56,785 complaints lodged in the state.
In 2011-12, the TIO carried out 79 systemic investigations.
The TIO's powers were recently increased, with the organisation now able to make binding determinations to providers on cases up to $50,000 (up from $30,000) and make recommendations up to $100,000 (up from $85,000).
"An increase in powers is always a good thing for consumers who cannot resolve the issues they are having with their service providers," Cohen previously said.
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