Last fall, the Ministry of Internal Affairs and Communications set guidelines for "unlocking" mobile phones. Until now, in principle, a handset sold by one of Japan's three main mobile communications companies — NTT Docomo, KDDI and SoftBank — could only be used for that particular service, meaning if you wanted to switch companies, you had to buy a new one.
The guidelines were to go into effect at the beginning of May. The changes will only affect new phones, and they can only be unlocked — at no charge if done online — for their original owners. Moreover, customers of each company will have to wait six months after purchasing their phones to get them unlocked.
Which manufacturers this will affect and how mobile phone fees and contracts will change isn't clear at the moment, but it seems the guidelines were issued in response to complaints from consumers about the high cost of mobile communications in Japan, the idea being that unlocking phones will spur competition. The purpose of locking the SIM cards — those devices that determine which network the phone connects to — is to keep customers aligned to particular carriers, which mandate two-year contracts for services.