My 12 year old son's mother gave him a new mobile phone as a gift but it was under contract to her. He has since swapped the phone for other items. She is now demanding the phone back and has gone to the police who are telling me they will arrest my son for theft and arrest me for being an accessory (as it was swapped to someone he met through me). She has since canceled the phone which is a breach of contract. As the phone was a gift to my son, is it his to swap if he wants to? Or is it theft as the police are saying? Any help would be much appreciated.