Consumer complaints about mobile roaming charges have dropped, but the disputed amounts for complaints are increasing, with one customer lumped with a $147,908 bill after a European holiday, according to the Telecommunications Industry Ombudsman (TIO).

Around $8 million in bills about global roaming were disputed in the July to September quarter this year.

New complaints to the TIO dropped 10.8 per cent in July to September this year to 37,777. New complaints are now 26.1 per cent lower compared to the same period last year.

Mobile service complaints dropped 11.4 per cent in the period compared to the previous quarter, a 35.6 per cent drop compared to the same period last year.

However, complaints about mobile phone services still make up most of the complaints to the TIO at 57.5 per cent.

Complaints about customer service accounted for 23 per cent of complaints, followed by billing and handling (19.8 per cent) and faults (17.9 per cent).

Complaints about network coverage increased 4.2 per cent, following five quarters of reductions. Disputes about credit defaults also increased around 5 per cent and disputes around consumers being notified about impending defaults increased around 10 per cent in the July to September quarter.

The TIO said the minimum credit default amount consumers can be listed for is under review, with the TIO looking to increase the minimum amount for a credit default from $100 to $300 in response to a discussion paper released by the Attorney-General on credit regulations in May this year.

The TIO recently revealed complaints about Optus increased 47 per cent, while complaints about Telstra dropped 21 per cent in 2011-12.

Optus complaints were driven by mobile-related services, according to the TIO, such as faults, inadequate spend controls and disputed Internet charges.

Complaints about Vodafone 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.