This Phone warning light has no lamp inside any more, just everlasting high intensity red leds.
The unit is powered by a 12 volt DC 1A external power supply that is included in the delivery.
What you only need is one stereo cable coming from a latching switch that goes directly hard-wired to a barrier strip inside the Phone light. Or if you have a GPO output from your equipment (GSM) that can also do the job.
The power adapter will also be directly wired to the barrier strip inside the unit.
There is a Cable entry hole and key slot holes on the backside for wall mounting.