
My G1 has a full qwerty keyboard, touchscreen, and a trackball, and as long as I have WiFi access, internet is free, but it can still access 3G if needed. So it can basically be used as a portable computer. The Droid seems to be the Android phone with the most promise these days.
It is possible to Root, much like Jailbreaking an iPhone, though I haven't Rooted mine because I haven't had the need.
There is an Android market for apps much like Apple. It's not as big, but Android is an open OS, and I usually support stuff like that since the possibilities are virtually endless. Because of this, there should theoretically be more customizability, unlike the proprietary nature of some *ahem* other companies. I'm in Canada, with Rogers pay-as-you-go, using an unlocked G1 from ebay, so I got no clue how this stuff works in Japan.