shorting the line is what old phones used to do to put the line on hold. Since the on hook state is dertermined by the line current, a short looks like the phone is off the hook to the telco. I don't remember the box's name, but there was one that exploited this. I can't remember exactly how it went, but I believe you would have someone call you, then you would use a resistor to decrease the current going through the phone, so the telco would think the phone was still on the hook when it actually wasn't. it would allow you to talk for like 15 minutes or something (before the telco would stop ringing, which is normal). quick search on google didn't come up with anything. anyone remember the name of this box?
the available current is so low (9v at 600 ohms, I=E/R, I=9/600=15mA) that you couldn't power a christmas light with it. but, you could easily set up something like you're saying, just with lower power components. I like the idea >