Radio Configuration -> Radio Wide
General -> ARS User Login Enable: CHECK
General -> Soft ID/Username: ANY VALUE, but needs to be in the Data User List of any other radio that wants to send a message to this one
General -> PIN/Password: ANY VALUE
Data: All settings can remain default, including Subscriber IP Address, which can be the same for each radio. However, the TMS operates a little quicker when you assign a unique IP address, on the same subnet, to each radio. For example, 192.168.128.z

Radio Configuration -> Controls -> Buttons
Data Button: TMS

Conventional -> Conventional Personality -> Conventional Personality X
Rx Options -> Rx Voice/Signal Type: Mixed Mode, or ASTRO
Tx Options -> Tx Voice/Signal Type: ASTRO
ASTRO -> ASTRO System: Y

Conventional -> ASTRO Systems -> Astro System -> Astro System Y
General -> Individual ID: Can be whatever you'd like, but needs to be unique to each radio you want to participate in TMS
Data -> Packet Data Compatible System (PDS): CHECK
Data -> Auto Generate IP Address: CHECK
Data -> Auto Generate Target IP Address: CHECK
Data -> Packet Data Mode: Direct
Data ->Text Messaging Service: List Only (for model 2 or 3), or Unlimited (model 3 only)
ARS -> Automatic Registration Service Enable: CHECK
ARS -> ARS Mode: Non-Server

Radio Configuration -> Data User List
Preset list of radio Soft IDs, where the "Data User Information" field matches the Soft ID/Username for each other radio you want to participate in TMS

Radio Configuration -> Quick Text Message
Create records for preset text messages. You have to use these if you have a model 2 radio, but makes it easier even with a model 3.

Zone Channel Assignment
Each channel you want to have the ability to exchange text messages on must be assigned to a Conventional Personality that's configured with the settings above.