Years ago, a vendor suggested this solution to the Message waiting lamp issue on an SX-2000 + DigitalSpeech voicemail system connected via COV ports.
Use Superset5(COV)phones to send feature access codes to turn off the message lamps. It seemed like a pretty jugheaded idea, but since we had extra ports, I went with it and put a set in the Phone Room and one on my desk.
With informed hindsight, I'm sure it was just that the SS5's had the same COS as the VM ports, but it worked.
A side benefit was that with the ass-ugly phone on my desk instead of the nifty white 430 I had previously, I didn't have to put up with status-hungry users whining for an upgrade from their black 410's. (My prime line was a 1937 North Electric Model 20 rotary phone with a sticker labelled: Y2K PHONE).