The communications ministry has released a draft guideline that urges mobile phone operators to remove the lock that limits the use of handsets to the carrier's own network but doesn't compel them to do so.
Under the guideline released Wednesday, mobile carriers would be allowed to select which handsets may go on sale without carrier-specific locks, called SIM locks, and SIM lock-free handsets would be put on the market next April at the earliest.
The ministry decided against mandatory measures because users of the current generation of handsets sold in Japan would likely face problems even if SIM lock removal is made available.
One of the three main carriers, KDDI Corp's au, uses a technology standard incompatible with others, and removing the lock would not allow au subscribers or handset owners to switch to NTT DoCoMo or Softbank Mobile services or handsets.
Services available for unlocked phones would also likely be limited to voice if carriers are switched. Mobile Internet services are offered through proprietary technology protocols specific to each carrier.
The ministry said it is planning to finalize the guideline by the end of June after inviting public comments until June 23.
The ministry has been urging mobile carriers to remove SIM locks, a measure that boosts convenience for consumers as they may be able to choose any combination of handset and carrier.