On 'MY' phone.. if someone texts me.. I can save it on 'MY' phone for however long I wish, even if the sender of that text cuts up his own sim card, runs over his own phone, etc. They found SS's texts TO DM, on DM's phone, even though SS had purchased a new phone.
Exactly. The texts will reside on both phones. If using Apple's iMessage, those texts would also reside on their iPads or MacBooks, if they own them.