The method to do so is already on your person. The cufflink shall offer you a plethora of ways to contact those within the city, Use it by way of pressing a button on the side to activate it.

( Emet-Selch motions to his wrist with an open palm. It certainly doesn't look like a communicator at first glance, an understandable oversight. )

Do try to send your messages during the waking hours.