Using emoticons in text messages could cost you lots of money without you realising.
Lots of people have complained after racking up huge bills for including things like smiley faces in their texts.
The problem has been affecting people using older models of some mobile phones. When emoticons were used in a text message on those devices, some phones converted them into MMS (Multi-media service) messages which can cost up to 40p per message.
A woman in Scotland was recently charged £1000 for her phone bill, after using emoticons in her texts.
The mobile phone company O2 recommended that people don't use emoticons in text messages to make sure they avoid extra charges.
Experts say mobile phone operators need to be clearer about MMS charges and are advising that people check their bills regularly and use free-messaging services instead, if they want to use emoticons.