0120 numbers are toll-free numbers where the receiver pays call charges. Callers pay nothing; the receiving company bears all costs. Provided by NTT Communications as "Free Dial," they consist of 0120 plus 6 digits (e.g., 0120-XXX-XXX).
0120 numbers are ubiquitous for corporate customer service: support, orders, information requests, and complaints. Eliminating caller charges lowers the barrier to contact. TV commercials commonly announce "Call 0120-XXX-XXX" leveraging this system.
Note that some 0120 numbers don't accept mobile calls. If the company hasn't enabled mobile reception, callers hear "This number cannot be reached." Use the mobile-specific number (often 0570) listed on the company's website instead.
0800 numbers (Free Access) offer similar toll-free service, introduced to address 0120 number exhaustion. See Free Dial vs Navi Dial and Free Dial business benefits.