Last time, when I did not have it, I had to use hand signals and loud exclamations like "Go" and "Whoa" to get the message across. While it worked surprisingly well, the finer points had to be saved for the conversation in the paddock.
I got the Chatterbox central unit on Craigslist last week, and the headsets arrived from an online vendor today. Tested the whole set together, and it works. Now this only makes me want to go back to the track sooner, while I got another three weeks to wait.