SMARTPHONE users that punctuate their text messages with a smiley face could be paying twice for a single text.

last night admitted that consumers that used emoticons or smiley faces that contained bullet points could be paying double because the punctuation was splitting text messages in two.

The billing issue was first discovered by a Melbourne man who found that he had been charged twice for every text message that contained a bullet point.

Telstra said the bullet point and emoticons caused a coding issue which limited the number of characters the message could contain.

Its Terms of Service say text messages that contain non-standard characters like bullet points, umlauts and emoticons, and were more than 70 characters in length would be charged more.

"We charge for each group of 67 characters or part thereof that contains non-standard characters,'' it reads.

The spokesperson said: "It is not a handset or a phone company rule, but rather the technology used to send messages. We do make this information on how we charge customers for SMS available and most phones allow customers to see how long their messages are.

"The issue reportedly only affects iPhones and Samsung smartphones."

Apple and Samsung declined to comment.