In a mobile communications system 10, a message is sent to a mobile terminal 16 which transmits an acknowledgement signal if the message is received. If the system 10 does not detect an acknowledgement signal, it transmits a high margin notification signal to the mobile terminal 16 to notify the terminal that an attempt was made to send the message. When the mobile terminal 16 has received a notification signal and subsequently comes within range of lower margin signals from the system, it sends a registration signal to the system. The system may then retransmit the message to the mobile terminal 16.