Good morning, Reggie;
Your request really is not that difficult, but I admit that I do not know of anything specifically designed to perform this task. However, . . .
One possible way to do it is with an old telephone answering machine. Many of those systems used a three or four digit code that was sent from the calling telephone to begin a telephone message playback process to retrieve messages from your machine while you were not at home. It should be possible to modify one of those old machines that accepts that code, and instead of starting the tape recorder in playback mode, have that same internal signal sent to a latching relay that would control a 120 VAC power or Mains power relay, contactor, triac, or similar device that would turn on the circuit for the power to your darkroom. A latching relay does not require a constant application of electrical power to hold it in the contacted or "set" position. There should also be a manual push button switch on the other side of the control coils for the latching relay to move it from the "set" position back to the "reset" position to be ready to receive the next telephone call.
Contact me if you would like to discuss this. And, I agree that not everyone is "unemployed." Some of us are retired. Work as long as you can. You will not really appreciate a job with its predictability, familiarity, and stability in your life, until you no longer have it. Life in "retirement" can be wild. I am busier now than I ever was when I was "gainfully employed" and still had a useful purpose in life. And I really do miss holidays, weekends, and vacations.