http://www.flyertalk.com/forum/showthread.php?t=544697
Post #5 and beyond.
Suica and PassMo (and I guess, Icoca?) are interchangeable now
While Suica is compatable with ICOCA and PASMO, PASMO is not comptable with ICOCA. To spice things up, ICOCA is comptatable with PiTaPa, but Suica even though comptable with ICOCA, is not. They're working on fixing all this up by 2008 or abouts.