it would depend on the type of arrestor your planning on using..
Gas Discharge Surge Arrestors of 150 volts or less will be added protection. other types varistors, thermistors and the like would have small effect in protecting the communicator.
this all assumes the cable guys did the proper grounding arrestors on the cable inlet to begin with.. if not just wave the ole NEC 70 electrical code at em.. article 800
Not to go overboard but as more and more cable modems get installed and POTS go away a question comes to mind.
For the past quite a number of years I have installed with every system a lightning surge protection on the phone line. Now with the Digital Voice and the modem hanging on the cable is the surge protection still a desired thing to do or even an issue??
Thanks for any thoughts.