Hello? Is anybody out there listening?

Hidden charges: In week four of our consumer campaign, Nicholas Pyke tries to untangle the array of mobile phone tariffs

A trip to the mobile phone shop leaves most of us needing therapy. The big operators run so many hundreds of tariffs, deals and packages that their tactics have been condemned as "confusion marketing". So Eamonn Carlin from Belfast was quite relieved to hunt down a good deal with Firstpoint, a company owned by the giant Vodafone.

That was until he found that the contract he signed had been changed, without warning. Suddenly 0845 numbers (and his telephone bank) were banned from his monthly free-call allocation. Then the price of texting abroad was raised by 150 per cent, to 25 pence a message - a serious issue in Northern Ireland. Eamonn's friends and relatives in the Republic will be hearing less of him until he ditches Firstpoint, as he now promises to do.

But, whichever operator he turns to, the 25-year-old knows there is no chance of escaping hidden charges. "These network providers seem to be the eels of the business world - always wriggling, slipping through the regulatory net, and trying new ways of extracting even more money from Joe Public," he complains.

He is not alone. Of all the rip-offs that our Hidden Charges Campaign has tackled, none has attracted so many indignant lettersas mobile phone charges.

The National Consumer Council has every sympathy. The first problem, it says, is comparing one deal with another, because access to the networks is sold as a package. So everything, from the cost of the handset to the price of texting and voice messaging varies from deal to deal. Even the mobile phone companies admit that the jungle of different tariffs is a problem.

The second major pitfall is the enormous cost of taking a mobile abroad. As the Consumers' Association puts it, "fail to do your homework and you'll be paying the bill long after the tan has faded". Vodafone pay-as-you-go customers, for example, pay £1.99 a minute in Australia just to receive calls from the UK. Orange pay-as-you-go users fork out £1.20 a minute to ring the UK from Spain.

Then, even when you think you have a deal, the phone companies may decide otherwise and amend the contract to suit themselves. "I was told that the changes had come in a month earlier," Mr Carlin says. "What bothered me was not the money they were taking from me, but the fact that they changed call charges during a contract without notifying me first.

None of this, however, begins to touch the biggest hidden cost, which is the long-running scandal of "termination charges". The NCC explains that every time you call a mobile phone on a different company, or ring any mobile phone from a landline, the network you link up with levies an enormous fee. This amounts to 40 per cent of a call from a mobile, and 60 per cent of the cost from a landline.

Even though Oftel, the phone regulator, has been demanding hefty reductions for the past two years - resisted by the operators in the courts - there has been no more than a 15 per cent cut so far. It went through last summer, but some companies, such as Orange, are not passing even that small amount on to the consumer. "Termination charges are a massive subsidy from people restricted to landlines, who are disproportionately elderly and less well-off, to the mobile phone companies," says Neil Crowther, senior policy adviser to the NCC.

To make matters worse, Oftel regulates only the "wholesale" market - the fees charged between companies that form the structure of the industry. So it is powerless to instruct the operators to give consumers a better deal. A new telephone ombudsman has been created, but two of the big operators, Orange and T-mobile, have so far failed to sign up, leaving only Vodafone and O2 on board.

In the absence of proper controls, the Consumers' Association recommends a series of measures, starting with copious research. If you go abroad, it suggests you find out which the cheapest network is, and manually select it on your phone. Or stick to text messages. In some countries you would be better turning off the voicemail, or even buying a new SIM card from a local company to use on holiday.

Both Orange and Vodafone agree that the plethora of different prices has caused confusion, and both say they have now introduced simpler price structures. A Vodafone spokeswoman said: "We're sorry Mr Carlin was disappointed with the service. We amend our tariffs to make sure we offer the best overall package for customers. And we're sorry if he feels he wasn't informed beforehand of the changes."

If, meanwhile, you feel like making a complaint, make sure you check the contract first. A call to customer services could cost you.

Your views

In Hidden Charges we've featured covert rip-offs from restaurants to banks. Now, here are some of your bugbears:

I had my car serviced a few weeks ago. When I got home I found an unopened can of oil and a few tissues in the boot. When I checked my receipt I discovered a "1 litre top-up kit" hidden between the oil and the brake cleaner. I had been charged nearly £8 for something which I hadn't asked for and didn't want.

David Lee, St Albans

One of the worst scams I have come across is hospital trolley phones. My experience was of feeding a monster that swallowed money so fast - even on local calls - that I had to keep a cup by my bed and beg loose change from visitors.

Jean Brodie, Cinderford, Glos

I went with five friends to a sushi bar. We had to serve ourselves from the conveyor belt. But when the bill came it included a charge for service. The small print on the menu revealed that the booths we were sitting in incurred a 10 per cent service charge if occupied by three or fewer, or six or more!

Anne Tierney, Glasgow