A consumer watchdog has slammed mobile operators for the use of the word 'unlimited' when advertising mobile data tariffs.
A Moneysupermarket.com survey showed that a quarter (24%) of people did not know if they had a download limit on their internet service, while the 54% of people who knew there was a limit didn't know exactly what the limit was.
The big five operators all provide tariffs which include voice, text and data, with some advertising that they include 'unlimited' data.
However, a fair usage policy often applies, which caps the amount of data a consumer can use, meaning they may receive a warning from the operator if they go over the allowance.
The term 'unlimited' varies depending on the handset which comes with the tariff.
T-Mobile's fair usage policy for Android handsets is 3Gb a month, while non-Android handsets such as the Nokia X6 are 1Gb.
Meanwhile, Orange gives its iPhone customers 750Mb data with the handset. Other handsets come with free push email or 500Mb of data.
O2 has no data cap and instead has an 'excessive use' policy to prevent intense downloading.
Vodafone used to advertise 'unlimted tariffs', but now offers 1Gb data on its iPhone tariff and 500Mb for most of its internet-enabled phones including Android.
3 advertises all of its tariffs as 'unlimted,' but has a 1Gb data cap on all internet devices.
Mobile and broadband manager at moneysupermarket.com, Mike Wilson, said: 'People need to be aware that unlimited doesn't always mean unlimited. If you delve a little deeper into the terms and conditions, most operators will have a fair use policy that comes into play when you exceed a set download limit.'
'Smartphones are commonplace these days and using your phone to download music, stream videos or surf the web has become standard activity. The most important thing is to know what type of user you are; light users should find it easy to stay under any limits but a heavier user with a 1Gb per month limit may find it a challenge to avoid incurring additional costs for exceeding it.'
'1Gb is roughly equivalent to a few hours of surfing and emailing, downloading two music tracks and watching two hours of video a week (e.g. YouTube/ iPlayer).'
See analysis in next week's Mobile (19 March).