The Astro25 Text Messaging Service is a protocol for text messaging between supported Motorola Astro25 and APX radios. It is part of the Q947 APCO Packet Data Interface flashcode option and is available on Astro25 radios with firmware R09+ and on all APX series radios. The service allows for direct messaging between radios and system infrastructure in a trunked radio environment, and for simple messaging between user radios in a conventional repeater or simplex environment.
Simple TMS Configuration
referenced from Akardam.net
to be added once I finish more testing and setup