Most APRS clients have the ability to send short station-to-station text messages. Messages may be passed through Igates, allowing long-distance contacts.
Short Text Messaging
An APRS message may be up to 67 characters long. Messages containing an identifier, an appended serial number, expect an acknowlegment from the address, and will be retransmitted until it is cancelled or times out.
Bulletins are addressed to "**BLN**" followed by a single-digit identifier. Bulletins are retransmitted several times an hour for a few hours, and typically contain time sensitive information like weather warnings.
Announcements are address to "**ANN**" followed by a single upper-case letter. Announcements are transmitted less frequently than bulletins and are usually not time critical.