A telecommunications carrier (MNO: Mobile Network Operator) is a major provider that owns and operates its own network infrastructure, including base stations, telephone exchanges, and fiber-optic networks. In Japan, four companies qualify: NTT Docomo, KDDI (au), SoftBank, and Rakuten Mobile, each holding spectrum allocations from the Ministry of Internal Affairs and Communications. Together, these four carriers serve approximately 200 million mobile subscriptions, forming the backbone of Japan's telecommunications infrastructure.
The key difference from MVNOs (budget SIM providers) is whether the company owns physical network equipment such as base stations. MVNOs lease capacity from carriers, so their coverage and quality depend on the underlying carrier's network. Carriers invest hundreds of billions of yen annually in infrastructure, expanding 5G base stations and upgrading network speeds. This capital expenditure is reflected in their pricing, which tends to be higher than MVNO plans.
Each carrier also offers sub-brands and online-only plans. KDDI's UQ mobile and SoftBank's Y!mobile serve as sub-brands, delivering carrier-grade connectivity at prices closer to MVNOs. NTT Docomo's ahamo, KDDI's povo, and SoftBank's LINEMO are online-only plans that achieve lower prices by eliminating in-store support. While technically not MVNOs, these plans compete directly with budget providers on price.
Mobile phone numbers starting with 090/080/070 are allocated to each carrier by the Ministry of Internal Affairs and Communications. However, thanks to MNP (Mobile Number Portability), users can switch carriers while keeping their number, making it impossible to identify a carrier solely from the first three digits. When choosing a carrier, consider coverage (especially at home, work, and along your commute), pricing plans, device lineup, and bundled services (loyalty points, streaming, etc.) as a whole. You can review the numbering system in How Mobile Phone Numbers Work.