The prices that UK mobile phone firms charge are highly contentious. Many consumers complain that it is too difficult to compare offers and that many charges are misleading. So how do you avoid being caught out?

What the salesman doesn't tell you

About 40 million people in the UK now have a mobile phone, but many of those are likely to be paying over the odds.

This is because the process of buying a mobile phone is so confusing.

There are simply so many different handsets, networks, deals and call costs to consider that buying the right phone for your usage and budget can be very difficult.

There is also a lack of independent advice on offer to consumers.

What should I watch out for?

One of the main ways to get caught out is to focus on cheap headline rates.

Many deals offer a rate of say 2p for an off-peak charge to the same mobile network or call to a landline.

However, it is highly unlikely that all your friends, family and business associates will be on the same network.

A large proportion of your calls will be to other mobile networks, which are usually much more expensive.

For example, Vodafone's Leisure 200 deal offers a 2p evening and weekend rate for calls to landlines, but it will cost you 30p off-peak and 50p peak to call another mobile network.

Pre-pay or post-pay?

You can either choose a monthly deal, which has a line rental charge and often inclusive call minutes; a yearly package or a pre-paid mobile, where you simply pay for the calls and no line rental each month.

The call cost on a pre-pay phone is usually more expensive than the cost you would incur with a monthly deal.

Monthly deals also have the advantage of including free call minutes usually during the weekend and for evening use.

However, subscribing to a monthly deal may not be economical.

If you are a light user you may be better off on pre-pay, because you may not even spend enough each month to justify the line rental charges which are typically between £15 and £30.

If you want to use your mobile phone abroad, and want to subscribe to a pre-pay phone you should ask whether you will be able to use the phone while you are abroad.

What happens if I want to use my phone abroad?

If you want to use your mobile abroad you may need to get permission from your network operator before travelling.

This involves calling customer services and asking for your phone to be enabled for international use. This function can be switched on remotely.

But you should also check to see that the specification of your phone is compatible with networks abroad. You will need a so-called "tri-band" phone if you want to make mobile calls in the US or Canada.

The GSM Association's website has a full list.

Once you arrive in another country, your phone will lock onto the network with the strongest signal.

While some will let you choose which one you can use, you will have to reset it each time you switch on the phone.

Isn't international use very expensive?

The cost of "roaming" which is the mobile industry's term for using your mobile outside your home country is currently under investigation by the European Union.

The reason why using your mobile phone abroad is so expensive is because you are charged twice: both for the cost of calls you make and for those you receive, including voicemail messages.

Roaming charges vary widely among countries and networks within those states.

To avoid charges, some phones let you divert calls to voicemail so that you pay only to retrieve the messages.

Frequent travellers to one destination often purchase a mobile phone for the country they are travelling to or purchase another Sim card which they swap when they arrive overseas.

But this is not always possible: some networks block this money-saving initiative.

Consumer groups are fighting for measures to reduce the locking of handsets to Sim cards, which will make it easier for people to switch networks. (from BBC NEWS)