Japan is in the middle of a mobile phone revolution thanks to a set of recently introduced regulations.
It used to be impossible for mobile phone users in Japan to unlock their handsets, which meant that every phone was tied to a network with no possibility of using them elsewhere. This effectively locked customers into one of the big three service providers and stifled competition. This all changed when regulations were introduced in 2015, and it is now possible to use any unlocked handset with a Mobile Virtual Network Operator (MVNO).
The advent of Japan MVNO carriers is great news for those looking for a cheaper alternative to the traditionally lengthy and costly contracts available from the incumbent networks.