Alternately, someone who has one of those plugs and a decent ohm meter can measure the actual resistance and post that information here. Then you can make up a power cord to a terminal strip in a plastic box, with the resistor in series with the Hot lead, to an output cord that can be connected to the phone.
Also you definitely want these AC plugs plugged into an outlet equipped with a GFCI (ground fault circuit interruptor) right at the outlet, "just in case."