iPhone can natively read these documents if you're sent an e-mail with an attachment. Unfortunately there is no separate application to view them, let alone edit them.
There, however, are a host of
web apps to look through. Some, like
in.solit.us, store your docs on a web disk and allow you access to them from your iPhone or other mobile device.
Apple has
announced there will be a software dev kit (i.e. native iPhone apps) but that won't be released until February. Naturally, apps won't come until substantially after that.
-K