when it comes to signal, AU has the strongest. Even docomo can't beat them on that. Softbank has the crappiest signal. But why I stayed with Softbank?
its because of: GSM, 3G, International Support ( Roaming and Multi-Language support ).
There are lots of cool fones in AU but does not have the feature above. They even have a fone with a internal HD about 4G capability for music support, but the other capabilities of that fone is crap and does not have a multi-lingual support. AU's 3G lines of phones as of the moment is limited, but their software support/application are cool. But their dometic lines of fone are really amazing but be sure to check if it has multi-lingual support cause most don't.
Docomo, well just read the other post above. Their phones are really cool, and some even have free dictionary software ( upgradable ).
The last time that Ive checked with Docomo, their 3G lines are really cool but still no GSM support and automatic international roaming. So if you go outside japan your phone is totally useless but is good as camera or alarm clock. And their plan is a bit pricey especially if you get the latest release.
Right now am sticking with softbank, since most of the ppl that I talk ( too much ) are all softbank users, so its really convenient ,its FREE and UNLIMITED. am only paying the packets that I use with the none-softbank user and my international SMS use
Im using white plan, and I like it better with the pre-define packages, cause I can use or select which feature I like.
So am paying 2200 ( white plan+insurance/features+phone ) + packets used (optionally). So most right now am paying not more than 3500 per month. I don't used fone for surfing the net, except for train schedule if necessary
So if you love surfing the net on your phone, cute and cool phone applications, go with AU or DOCOMO.