PHONE users are being warned to be on the lookout for hidden costs related to sending emojis via text.

Some users have found they've been charged for sending multi-media messages (MMS) after having their texts automatically converted into an MMS, because they include emojis or exceed character limits.

MMS messages are not always free in a users plan. 

Phone networks EE and O2 charge up to 40p for an MMS.