Navi Dial is a nationwide unified number service starting with 0570, provided by NTT Docomo Business (formerly NTT Communications). Since businesses can receive calls from anywhere in Japan using a single number, it is widely adopted by call centers and public service counters. The benefit for businesses is the ability to unify phone numbers across multiple locations and automatically switch call destinations based on time of day or day of the week.
The biggest difference from Free Dial (0120) is who bears the call charges. With Free Dial, the receiving party (business) pays, making calls free for the caller. With Navi Dial, the caller pays the charges. Moreover, since Navi Dial is excluded from mobile phone free minutes and unlimited calling plans, it effectively functions as a premium-rate number. Call charges vary depending on the line you call from (landline or mobile) and your plan; calls from mobile phones tend to be notably more expensive, and the cost grows the longer the call lasts.
What trips callers up is that Navi Dial charges apply even to subscribers of unlimited calling plans. The number itself tells you nothing about who pays, so it is safest to treat any number beginning with 0570 as caller-paid. Businesses adopt Navi Dial for the cost advantage of passing charges to callers and for the convenience of a single nationwide number. Conversely, toll-free numbers (0120/0800) cost the caller nothing, which lowers the barrier to getting in touch.
A practical tip: many businesses publish regular landline numbers (starting with 03 or 06) alongside their Navi Dial number. By searching the company's official website under "Company Information" or "Contact Us" for a landline number and calling that instead, you can make the call within your unlimited calling plan. If only a Navi Dial number is available, it is wise to prepare your points concisely before calling to minimize call duration. You can review the detailed fee structure in the Free Dial vs. Navi Dial comparison.