While 888-276-5255 is Optimum's best toll-free number, there are 8 total ways to get in touch with them. The next best way to talk to their customer support team, according to other Optimum customers, is by calling their 800-877-8849 phone number for their Cablevision Customer Service department. Besides calling, the next favorite option for customers looking for help is via 800-877-8849 for Cablevision Customer Service.