The great mobile rip-off: Worst offender revealed

Australian mobile phone users are getting ripped off by carriers offering contracts that provide less data at a greater cost, it has been found.

Consumer group Australian Communications Consumer Action Network says advanced mobile phone technologies have led to people using more data-consuming services such as video calls.

This puts pressure on network infrastructure, causing congestion issues.

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The consumer group has also found that the country’s three biggest mobile phone providers have slashed the amount of data offered in their plans, with Optus being the worst offender.

Fairfax reports Optus customers on the $80 cap get two gigabytes of data and $850 of credit a month - half the data and $50 less credit than was offered under last year's $79 cap.

Those on the $99 Timeless consumer plan get 2GB less.

Telstra and Vodafone have made similar moves with Telstra's plans noticing the smallest reduction in data.

Fairfax reports it offers 500MB less in its $60, $80 and $100 plans, and the same 3GB of data in its $129 plan.

Elise Davidson, a spokeswoman for the Australian Communications Consumer Action Network said one of the biggest issues was the customer confusion over mobile phone plans data estimates.

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Fairfax quoted Davidson as saying that many customers underestimated the data they would use and were hit with massive bills at the end of the month.

Optus has said the reductions in data would not affect most of its customers.

''We recently conducted a survey amongst our customers which showed the average amount of data being used per month is less than 500 megabytes,'' managing director of marketing Michael Smith was quoted as saying.

''With this in mind, we've refreshed our range of post-paid plans to reflect current customer trends.''

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