We present the results of a study on how Swedish children aged 10--12 use their mobile phones in public indoor and outdoor settings, and in particular how these are taken into use in unsupervised social play. Through a combination of ethnographic observations and focus group interviews we report on how existing mobile phone functionalities were handled in these settings, as well as how the children themselves described their own and each other's mobile phone usage. Our findings illustrate a general pattern of appropriating and utilising commonly available technical features to extend existing play activities, and also to invent new ones based on the functionalities that they discovered. An important observation was also the extensive sharing of media content, which played an essential role in social interactions.