"400 Toll-Free Service," also known as "National Unified Access Number Service," is a 10-digit national access number provided by China's three major telecom operators (China Telecom, China Mobile, and China Unicom) to enterprises. It allows nationwide calling without the need to dial a local area code. Enterprises simply need to link the 400 number with their existing physical phone numbers (landlines, mobile phones) to receive incoming calls routed from the 400 line through their original landlines or mobile phones. Currently, it is widely used in various industries for pre-sales, after-sales, and service consultation.Link the 400 number with the company's original physical phone numbers (landline, mobile) to receive incoming calls rerouted from the 400 line through the company's existing landline or mobile. Currently widely used in pre-sales, after-sales, service consultation, and other aspects across various industries.