Consumer group Which? is warning smart phone users that watching a film on your phone while abroad could cost you nearly £4000.
Data tariffs in certain countries are so high that astronomical bills can be run up by watching media on phones or tablet devices.
Countries including Thailand, Kenya and Malaysia can charge up to £10 for one megabit of data streamed, meaning that a three-hour film could cost you in the region of £3600.
“Using your mobile overseas can be hugely expensive but there are things consumers can do to keep costs down, like using wi-fi where available and turning off data roaming,” said Richard Lloyd of Which?
The group also advised buying a local pay-as-you-go sim card where possible too, in order to reduce costs.
Ensuring that data roaming is switched off will avoid applications using data automatically, whether you're using the device or not.
A cap on data roaming charges is coming into effect in the EU this month, with providers not being allowed to charge more than 68p per megabit, but the cap does not extend to countries outside the EU.