I've attempted to use an N900 as my main phone in Japan but it wasn't really much of a success. MMS - I got MMS working with fMMS on the Softbank network but I often had problems where I couldn't receive/open MMSs from Au or Docomo users. Didn't happen all of the time but a lost message isn't good. Other problems include not being able to check the server for messages which haven't yet been pushed to the phone yet (I don't know if that has changed in fMMS yet).