Commuter passes (ICOCA, Suica, etc)

Hi.

I have a question about commuter passes. I live in the Hiroshima area, and use an icoca card on the trains.

Later this year, I will be living for a little over two weeks in Tokyo. I figured I would buy a Suica card when I got there. However, I have recently been seeing posters in JR trains talking about how there is increased compatibility between SUICA and ICOCA cards (and some other card. Odd posters with the Suica penguin, the Icoca duck, and some little yellow bird-thing that is the mascot of the third company all skydiving together). My Japanese isn't good enough to get anything more than the gist, so I'm wondering just how "increased" this compatibility is. Ie, can I now use my Icoca card everywhere in Tokyo that takes Suica, regardless of train type/company? And, would I be able to charge my Icoca card at train stations in Tokyo?

Just wondering. I mean, it's not like buying a card when I get to Tokyo would be hard, but 500 yen is 500 yen.

Thanks.

You can use the Icoca card on JR lines in Tokyo, but not the subways or private lines. It's up to you whether you think it's worth buying a Suica or Pasmo just to use on the non-JR lines, or whether you would be better off just buying individual tickets.