At the risk of redundancy, I'm going to echo what the others have said so far, and say that I had a hard time understanding exactly what was going on. Part of that was me just not being very audio-inclined, although you clearly made some (actually quite good!) steps to mitigate that by adding a phone key set I could use to compare, and allowing me to replay. That's an executory problem--I had issues executing.
My larger issue was conceptual. I got the idea from reading the instructions posted on your page, but had a hard time translating them into what I was supposed to do in gameplay. Normally when this happens, what I recommend is trying to ramp up with some escalation; perhaps starting with a board that's like a third or a quarter the size--even to the point where it's got a no-lose solution. Then, once the basic loop is clarified, you can start getting complicated with it!
It's a cool idea--although bizzarely not the first somewhat opaque phone switchboard game I've seen--and I hope you're able to iterate on it further.