Your scenario now involves a moving AP...hummmm...
I see simple OLSR announced subnets to the APs on the vehicles...what is the new problem?
You do know services can be announced too like an Asterisk server running on OpenWrt with OLSR?
Or simply announcing 5060/udp and having a VoIP app running...it should ring if called at sip:foo@<IP_address>
...but then again, these are regular phones...using the signal app...to connect to their global servers...when even cell towers are out???????