Finding the right mobile phone can be similar to matching the colours on a defective Rubik's cube.

Confusion is probably the most common feeling for those taking the plunge into the sea of mobile phone offers and deals, with a jumble of different rates, phones and rental charges being pitched at the prospective buyers.

The idea of pay as you go, is seen by many people as an easy and convenient option which allows them to be contactable without being charged the world (on a monthly basis) for the pleasure of this convenience.

Even though consumers are being offered better and cheaper deals under longer term contracts the sales of pre-paid phones have stayed strong, with a spokeswoman for Eircell saying that sales of its Ready to Go range continue to rise.

Nearly half of all Eircell's sales are made up of pre-paid phones (47 per cent) while around 20 per cent of Esat Digifone's sales comprise its pre-paid version, Speakeasy.

Mr Stewart O'Reilly, of Glasnevin Communications, says that card or pre-paid phones are basically only a step up from a pager and that anybody using them should not be making calls at peak times because the rates per minute are so expensive.

A conversation of five minutes could cost you up to £4, with rates of 75 pence (Speakeasy) to 80 pence (Ready to Go) a minute the norm for peak times. the minimum spent of cards for pre-paid phones is £120 a year.

On the other hand, if you are more disciplined, you could get as much as 100 minutes for a £20 refill card with Eircell, while Esat will give you 80 minutes for the same price.

Although you can select your peak and off-peak periods, if you end up having a 20-minute argument over what to have for dinner, on a pre-paid phone at peak rates, it will cost you around £15, as much as 60 per cent more than the equivalent cost where you enter a contract to pay monthly charges.

Managing director of Dublin-based Total Recall Ltd, Ms Sandra Roche, said that pre-paid phones are ideal for teenagers, as a present for somebody at Christmas or for students on a tight budget - the advantage being that they do not allow the user to run up a huge bill that they cannot pay.

"However, cardphones are extremely expensive, and the problem is that if you run out of credit you can't make outgoing calls even in an emergency [that doesn't include 999]," she said.

Upfront offers, such as the Siemens C25 for £99 which includes line rental, 10 minutes free a month and rates of 20p at off-peak, 50p at peak are more suitable for the casual but talkative user.

According to mobile phone outlets, pre-paid phones make up between 30 and 50 per cent of all sales, with the percentage decreasing where companies deal more with business clients.

Another explanation for the popularity of pre-paid phones rests in the fact that contract or monthly-bill-based phones are simply not available to young people.

Eircell does not allow anybody under 21 to buy such a phone, and Esat has strict criteria for applicants which will normally see people without a steady job and a landline, normally those under 21, unable to get a bill phone.

While these policies may be sensible for both the customer and the company from the point of view of getting into debt, it also corners many entrants into using card-based mobile phones.

Total Recall's Ms Roche said that all staff at licensed Esat and Eircell outlets undergo training to ask the right questions of their customers and advise them properly on the best options. Both companies send people posing as customers into outlets regularly to make sure staff are truthful and licences can be withdrawn if they think customers are not being given a proper service.