I know exactly the modem you are talking about. Unplugging it, waiting 30 seconds and plugging it back in will not damage it, however since you use Comcast’s VOIP, that modem has a battery back up and won’t properly reset by just unplugging it and plugging it back in. You can either take out the battery as well and then hard-reset it, or call up Comcast anytime you switch devices on the modem. Your best bet is to buy yourself a router and only go through this once…