Consumer website MoneySavingExpert has received a large number of complaints about the issue which seems to affect older models of phones, including some Samsung and Apple handsets.

One woman managed to run up bills totalling over £1,000 after adding emoticons to text messages.

The problem is how the handset interprets the icons, known as emoticons or emojis.

In older handsets, the emoticons are converted into MMS (multi-media service) messages, which can cost up to 40p each depending on the network.

MoneySavingExpert said that users creating their own icons from full-stops, commas and brackets found they were converted into emoticons, running up the same charges.

Paula Cochrane told the Scottish Daily Record that she had no idea that the emoticons were being charged as picture messages.

She complained to her provider EE who blamed the manufacturer so she is taking it up with the Scottish ombudsman, an independent organisation that settles consumer complaints

Many people will have a contract which allows unlimited texts but this may not apply to picture messages and if you keep sending smiley faces you are going to burn up a lot of cash quite quickly.

O2 said it had seen other examples of text messages converting into picture messages. It said that there is not much that can be done other than not using them or the symbols.

Ofcom conducted a survey looking at all the reasons why people received higher-than-expected bills. Emoticons being billed as picture messages had affected 4 percent of those who responded to the survey.