The Japan government relaxed regulations on unlocking SIM of handsets in early 2017 and consequently MVNO (mobile virtual network operator) business has been in booming development in the Japan mobile communication market, with several MVNOs expanding retail networks and offering more services to attract subscribers.

The new regulations shorten the time taken to unlock SIM cards, which is helpful for portability of mobile phone numbers and facilitates mobile communication subscribers to shift from mobile telecom carriers to MVNOs.

According to Japan-based MM Research Institute, there were 55.62 million MVNO subscribers in Japan in September 2016, increasing 52.7% on year. Availability of inexpensive SIM cards (not locked with handsets) for sale or rent also pushes growth in MVNO subscription. According to Japan-based Seed Planning, there were 8.4 million users of such SIM cards in 2016 and the number will increase to 10.8 million in 2017, with Rakuten Mobile being the largest provider of such SIM cards.

More than 90% of MVNOs use NTT DoCoMo's mobile communication networks on lease mainly because rental rates are lower than those offered by SoftBank and KDDI au. While MVNOs compete with mobile telecom carriers, the latter have rental revenues from leased infrastructure increasing along with growth in MVNO user base.