WHY SIM is LOCKed by Carrier?
Japanese government used to operate infrastructure companies such as Electricity, Gas, Water, Post Office, Railways and also Communications. Now all the national owned companies shifted to operate as privatalized, for communications, they separated to docomo, au, and Softbank (Y mobile). However they set their sim locked so once users started they will stay because they cannot use other carrier.
Japanese Government realize that this is the main reason people cannot switch to low cost sim, they decided to order those 3 major companies to unlock the system. Now you can unlock the sim via online, but those who is not really good at online system such as over 50 generations usually go to the counter to unlock the sim, and they charge 3000yen for just unlock the sim.
How to Unlock?
Just click y!our phone carrier and type, then it will jump to tutorial youtube
Phone & Mobile
Japan Telecommunications⇨docomo
KDDIi⇨au
New Mobile Company⇨softbank
Trains
Electricity
