You can use Suica almost everywhere. The reverse is not true. For example, I live in the Tokai region and have a Toica. I can't use it outside of Tokai. I think eventually these things will even out, though. I was surprised that a Passmo card I got in Tokyo and accidentally used in Tokai worked.

But the golden rule in Japan -- make sure to carry enough cash in case you get into trouble :-)