An MVNO (Mobile Virtual Network Operator) is a carrier that provides mobile service by leasing network facilities (base stations and the like) from a major carrier (an MNO, or Mobile Network Operator) instead of building its own. In Japan these services are known as "budget SIM" or "budget smartphone" plans. In the quarterly telecommunications subscription data published by Japan's Ministry of Internal Affairs and Communications, MVNO subscriptions stood at 42.77 million as of the end of March 2026, giving MVNOs an 18.5% share of all mobile subscriptions. The same report puts Internet Initiative Japan at 24.9% and Optage at 8.2% of SIM-card-type MVNO subscriptions.
The biggest differences between an MVNO and a major carrier are price and speed. Because an MVNO does not build or maintain base stations itself, it can offer price tiers below a major carrier's standard plans. On the other hand, since it leases capacity, the bandwidth allotted by the MNO is shared among many users, so speeds tend to drop during busy stretches such as the lunch break or the evening commute home. If you stream video or play online games often, that slowdown translates directly into everyday frustration.
Choosing an MVNO comes down to matching your usage pattern. If your monthly data use fits within a few gigabytes, a small-allowance, lower-priced plan is enough. If you make a lot of calls, check whether a flat-rate calling option is available and exactly which calls the flat rate covers. If speed matters most, the sub-brands and online-only plans run by the MNOs themselves also belong on your shortlist. Those are supplied by the MNO over its own network, so they are not MVNOs in the strict sense. Whether leased bandwidth sits in the middle is the structural difference, and which side suits you depends on whether you put price or speed first.
Your phone number carries over through MNP, so switching does not mean giving up your number. If eSIM is supported you can complete activation without waiting for a SIM card to arrive, but support and the application steps differ from provider to provider, so confirm them before you sign up. Another approach is dual SIM: keep a major carrier for calls and use an MVNO for data, splitting the roles to hold costs down. You can review the switching steps in the number portability guide.
The low prices rest on not carrying base-station investment in-house. Many providers also operate mainly online without physical shops, and those savings show up in the price. In exchange, carrier email addresses (such as @docomo.ne.jp) are generally unavailable, and the number of shops where you can get face-to-face support is limited, which is worth checking before you commit. The same ministry data reports 771 primary MVNOs leasing lines directly from MNOs and 1,299 secondary or later MVNOs leasing from other MVNOs as of the end of March 2026, so the options are finely divided even by provider count alone.