My area doesn't really have farm units, but I was working on an IMT in Coonalpyn, and the numerous farm units were calling in on the phone to the base, advising that they were out there, who was on their vehicle, and where they were - only thing is that we didn't have an IMT form to put it all down on!!
I was speaking to a few other people from a different area who have a different sort of system, in that farm units turn up at a call, and "attach" themselves to the appliance from their own area, and follow it around - they guys from that area seemed happy with the way that was working....
Pip