Communications systems require an “intersystem bonding conductor” that allows them to be bonded to the grounding electrode system (GES). Your GES must contain a bonding termination for this purpose [as per NEC Sec. 250.94], and it must meet the six requirements enumerated in 250.94. You don’t have to add this termination (if missing) to existing buildings or structures, but you still have to connect the intersystem bonding and the GES.
The NEC has slightly more than half a page of text about this. The goal is to prevent having two systems that are at different potentials from each other. Perhaps the most common NEC violation in residential construction is leaving exactly this situation. The telco or cable company drives a ground rod and considers their system adequately grounded, but there’s soil resistance between their rod and the service a few feet away. This makes flashover likely, thus explaining how so much residential equipment gets fried.
The danger is heightened in commercial and industrial settings, because (among other factors) there’s usually a significant communications plant and the system voltage is typically 480V not 120V.
