Unexpectedly large mobile phone bills are usually associated with using a smartphone for ‘roaming’ internet access when abroad, but it’s also a problem for people who don’t even leave the country.

The BBC reported last week on the lack of clarity from some mobile internet providers about the charges for monthly data deals once the allotted free amount of data has been used up.

The problem seems to stem from the use of “unlimited” — a word that has a crystal clear meaning to most people.

Mobile phone operators, however, have a different take on the English language and to some, “unlimited” can mean as little as 500GB of data a month.

So-called ‘fair use’ policies are often put in place to prevent customers from being charged from inadvertent excess data use each month.

Not all customers read the fine print of a 3G mobile broadband contract though, and some treat ‘unlimited’ as exactly that by downloading large files and watching data-hungry video on YouTube and BBC iPlayer.

The BBC report includes comments from the Communications Ombudsman and it calls on mobile phone operators to make three changes to the way they work:

Be very clear about what they mean by unlimited in the advertisements

Give advice to consumers so they know when they’re reaching their limit

Give advice on the amount of data that’s being downloading

[BBC Newsbeat]