About one in four of the 2000 consumers surveyed for Deloitte's Mobile Consumer Survey 2017 admitted to 'fairly' or 'very' often using above their cap's data allowance.

And more than half of 25 to 34 year olds have exceeded their limit at least once.

This is despite new phone users with a data limit above 10 gigabytes doubling since 2016, report author and leader of strategy consulting practice Monitor Deloitte Jeremy Drumm said.

"And 60 per cent of new plans purchased in 2017 had a limit exceeding three gigabytes," he said.

"And yet people are still regularly blowing limits, resulting in consumers paying approximately $30 million a month extra to their operator."

Despite the dollar figure attached, it was calculated to be 33 times cheaper to go above plan in 2017 than four years ago.

One particular area of heavy phone use was streaming content - with the number of people streaming video and watching live TV on their phones tripling in the past 12 months.

A quarter of 18 to 34 year olds watched live TV on their mobile on a weekly basis.

About 40 per cent of survey respondents listed unlimited data plans as important when selecting an operator, even though there were no unlimited plans available when they survey was undertaken in May and June 2017.

And despite larger plans being offered, the percentage of those who 'churned' to a different provider increased from 15 to 18 per cent. This was particularly high in the younger cohort - with one in four 18 to 22 year olds switching in the past year.

And with the increase in streaming comes a need for larger data caps, and increased offerings from telecommunications companies.

Comparison website Finder's 2017 Excess Data Charges Report released in October found the average Australian is on a six gigabyte data plan. Gen Ys are typically on seven gigabytes, while Baby Boomers on average have four gigabytes on their plan.

And, collectively, Australians were paying an additional $259 million in excess mobile data charges for exceeding their caps. On their estimates, about 20 per cent of Australian adults regularly exceeded their data allowance - with Gen Y being the worst offenders.

With some telcos charging $12 or $13 per gigabyte extra, this could add up to hundreds of dollars a year, Finder spokesman Alex Kidman said.

"While the lower limit and smaller 24 month repayment on a new iPhone might seem more friendly to our hip pockets, the reality is paying excess data charges is more expensive than choosing a more generous data allowance," he said.