One problem with the Nuvi/OT2M setup that needs software adjustment.
If you send a msg "-ve7xxx-9 this is a test " and the ve7xxx does not reply ...ACK acknowledge at the AX.25 level ( radio off, out of contact with RF APRS network )
the OT2M attempts to send the msg forever.
Use the NUVI messaging service to send the following command to OT2M
"--retries 4 " (note space between retries and the 4) . The will limit the msgs sent without reply to 4 TRIES.
The other way to modify OT2M commands is with telnet/hyperterminal to the OT2M and get into "cmd" mode like a KPC3 TNC
OT2M has quite a full command set ...other tricks are in there.