NTT DoCoMo Inc., despite being Japan's biggest mobile phone carrier, has been struggling against tough smartphone competition from KDDI Corp. and Softbank Corp., which is leading in that area.

But one edge that the cellphone behemoth — it has more than 60 million subscribers — still holds is in research and development. It devotes an average of more than ¥100 billion on R&D every year, about 2.5 percent of sales.

KDDI, which runs the au mobile phone service, spent about ¥32 billion on R&D in fiscal 2011, while Softbank invested a mere ¥860 million.