[Ron Ramirez]

When I lived in Evansville, once I cut the landline and switched to a cellphone, I discovered that the old, disconnected telephone drop made a great outdoor antenna.

I used a small capacitor in series with the red wire. No harm since the line was not connected. I would not use the red or green wires on a line that is still in service - it may affect your phone(s). But yes, if the yellow is actually part of the service drop from the pole, then use it by all means. I think I would still attach a small capacitor in series with the yellow wire, just in case...