For example, I'm getting a replacement for my all-time favorite phone answering machine, but the owner has forgotten the 3-digit code for remote message retrieval. :( I'm willing to try all 900 or 1000, probably while I'm watching tv, but only if I can get it to go quickly. So I need a test line to ring it directly, have the machine answer, and punch in the code.
Also I have 2 fax machines, one that sends and one that receives! :) I'm pretty sure I can get it down to one that does both.
I don't have two phone lines, and even if I did, I think things would run quicker with my own little circuit.
In the 7th grade, we had two candlestick phones and a dry cell to play with during ham radio club, and everything worked (except it didn't ring, but that was ok because they had no bells. :) )
Any help appreciated.