But have they banded together to the extent that you can send an SMS (aka "SkyMail") from one network to another yet? The standard reply to that sort of question has always been something like "no, we don't need to, SMS is for foreigners, we Japanese use e-mail" so it's good to see the Japan operators gradually moving away from their Galapagos mentality.
Sadly, a lot of the credit for that has to go to Apple, who were bold and assertive enough to demand to sell their products without the Japanese operators dictating terms and functionality. Contrast with Nokia, who behaved a bit like a nervous, apologetic, uninvited guest when trying to break into that market. I remember trying to get a Nokia on contract at DoCoMo. The sales assistant said "don't use foreign phones, they're all inferior to Japanese phones" even though many of the new wave of Japanese smartphones at that time were running Symbian (underneath a decent UI, which is how Symbian was designed to be used.)