I saw this software at the UK national hamfest this weekend:
http://www.crosscountrywireless.net/aprs_messenger.htm
I'm sure it will have an application - see SAT (no Ack frames) mode/
Also a piece of easy compatible APRS hardware.
i have no connection to the company but it seems to me to be an interesting bit of kit.
73 de andy G0SFJ