Many smartphone users travelling overseas have been shocked to return to huge bills, sometimes $1000 more than usual, because of global roaming.
About 300 travel centre agents who used smartphones such as iPhones or BlackBerrys while overseas in the past 18 months were surveyed by telecommunications company Vodafone.
Sixty-four per cent of them said they paid at least $100 over their usual bill when they returned; 6 per cent said they paid more than $500; and 3 per cent said they paid more than $1000 over their usual bill.
The costs of using smartphones overseas forced most users to change their habits but participants said there were some things they could not do without when travelling.
The most popular uses for smartphones overseas were keeping in touch with loved ones, with Facebook overwhelmingly the most popular application, followed by using maps, checking or sending emails and posting travel updates and photos to social networking sites, the survey found.
Often data was being used without customers realising, such as automatic software updates.
Roaming costs were an increasing concern for people as smartphones became more popular, said Vodafone general manager of business marketing Becky Lloyd.
"What happens is they've learned a whole load of new habits, like Facebook and maps and email.
"So people are doing it at home and then they go overseas and carry on that behaviour," she said.
Different apps used different amounts of data so it was often difficult to estimate just how much was being used, Ms Lloyd said.
Users were often scared abouthow much overseas data use would cost.
Vodafone had developed a system under which travellers could buy a data bundle and were notified when it had almost run out.
To avoid big overseas bills, Ms Lloyd also advised smartphone users to disable auto updates in Windows or anti-virus software, avoid websites with video or audio streaming, use the most efficient network, and block pop-up windows if browsing the internet.