I'll make the dangerous assumption that your referring to P25 radios.
TMS on the ASTRO25 platform unit-to-unit on talkaround without P25 infrastructure is absolutely possible (infact the non-infrastructure method also seems to allow the TMS data to flow across a P25 conventional repeater as well, assuming that the packet data mode is "Repeated" vs "Direct").
For direct:
- On the radio wide options, "General" tab, ensure that "ARS User Login Enable" is checked, and a Soft ID/Username and PIN are set.
- On the radio wide options, ensure the radio has unique IP address(s) set on the Data tab.
- On the ASTRO system "Data" tab, set "Packet Data Mode" to "Direct".
- On the ASTRO system "ARS" tab, ensure the checkbox enabling ARS is checked, and set the "ARS Mode" to "Non-Server".
This /should/ make TMS work direct over talkaround.