I was playing with the Dot telephone handset this afternoon. The cord has the red and green center conductors, just like a "regular" handset, but the handset didn't work with my desk phone. No signal at all. I started thinking (sometimes a dangerous condition) and realized that the Dot handset has the dialing pad built in, while my desk phone has a "dialless" handset.
So I took the handset over to the bedroom, where the clock/phone has the dialing pad in the handset. Same red and green wires in the handset cord. I plugged in the Dot handset, got a dialtone, was able to call out, and asked our son to call back. The handset did also work for an incoming call, but the light in the "rhino horn" did not illuminate with the ringing, and there was a short, loud buzz when I picked up the handset.
I don't know what telephone circuitry is in the base of the clockphone, but probably just the hookswitch. At least there is the possibility of using the Dot phone handset here in the U.S. I still need to find a speakerphone modem that uses the computer's sound card, rather than having its own mic and speaker jacks. Then figure out how to integrate the handset...