To no one's surprise, Korean handsets haven't really been offered in Japan. Samsung and LG Electronics would be the first two names that come to my mind when it comes to Korean handsets. Apparently that's what DoCoMo thought, too, as they announced today that they're jointly developing a FOMA handset with LG Electronics.
According to IDC (and the article), LG Electronics holds the #5 spot for worldwide phone shipments following Nokia, Motorola, Samsung, and Siemens. Notice how there isn't a single Japanese name there?
LG Electronics to develop FOMA handset with DoCoMo [Keitai Watch]