According to the Asahi, Docomo will start selling unlockable phones beginning with the summer 2011 lineup, which will include approximately 20 models, just under half of which will be smartphones.
Docomo will be the first of the three major carriers to begin unlocking phones, a move the Asahi speculates is designed to push softbank towards unlocking the iPhone. Mr. Son, who is Softbank's founder and CEO, and is also not stupid, has said he has no intention of unlocking the iPhone and is considering unlocking "one maybe two handsets as a test."
When the US FCC released the previously confidential iPhone details, many (including me) were surprised to discover that it does indeed support Docomo's FOMA Plus area (800 MHz W-CDMA). As far as I know, the only carrier in the world using 800 MHz is Docomo. So the iPhone is specifically designed to be fully compatible with Docomo. Japanese MVNO B-Mobile also supports FOMA Plus, making their iPhone SIM products more attractive.
Unlocked versus Unlockable
The summer 2011 phones are being described as being loaded with a SIM unlocking function. One of these phones can be taken to a Docomo Shop to be unlocked. Docomo has said all along that it will NOT unlock previous models. I am not familiar enough with Japanese feature phones to say for sure if it is reasonably impossible for Docomo to easily provide an unlock code, but it certainly is technically possible. Either way it don't matter 'cause Docomo ain't gonna do it. Period. Don't even bother asking at a shop because you will accomplish nothing, other than getting frustrated.
Small steps, but at least in the right direction.