A communication system for sending small data message is disclosed in which a user node receives data from a remote application program which is sent as a message to a central application program executing on a central hub. The user nodes sends the message to an access node using a first radio interface and the access nodes forward the message to a gateway node which relays the message to the hub over a second radio interface. The system also includes composite nodes which either implement access node and gateway node functionality, or switch operational modes between access nodes and gateway node functions. The mode switching can be triggered based on proximity to access nodes, or by instructions from a hub. The gateway nodes can implement a message storage function, and can be implemented as software defined radios.