I guess I worded my response about the aviation intercom wrong. I have the adaptors to let my iphone talk through the intercom, listen to music and all of that. I use that when flying and love it. However, nobody else I have been in driving formation ever has that set up so that is why voice didn't work.
Bringing 4 M35 trucks from Oklahoma City to here back in 2008 we tried using hand held radios with ear pieces for everyone else. I just plugged mine into the intercom. Some people could only hear and some could only talk. Texting always got through. Back in flip phone days wedging one of them in the gap between the windshield and the flip out glass was a great way to see when someone was texting. Since you couldn't hear it or feel it vibrate while driving. Kwai, Sermis and I did that bringing a M35 back from the Georgia Rally back in 2007.