The TNC in the TH-D72 can be used to send and receive AX.25 packet. Packet is still used in some parts of the country to send messages or for general chit-chat. Some amateur radio auxiliary communications group are using packet to handle traffic for served agencies.
This in addition to the primary purpose of the TNC and that is to send and receive APRS position reports, telemetry, weather data, and messages. APRS uses the AX.25 protocol.