My daughter keeps getting this message on her new phone. This is not a prepaid line. She has the family plan, which blocks any contacts outside of the pre-approved list. Could this have something to do with it? She keeps receiving texts from herself that's say she has insufficient funds to complete a message. She has not sent any texts recently, so this is not in response to something she tried to send. She hasn't used her phone in a few days and she received this message twice today.