Based on my limited adventures with the SDK, I think the way files are handled on the iphone right now is preventing any meaningful office applications from coming out.
Office application functionality would seriously boost the iphone's credibility as a business device. I really hope there is a creative offering getting around fo the limitations or a modification to the SDK on the way.
there are a few spreadsheet apps. I've tried "spreadsheet". the initial release had a view bugs in it though it seems to work well now for not to complex tables etc. It will export (via email) to excel.
Moblefiles which accesses iDisk (if you have MobileMe) allows you to read Office documents, and the developers are planing a release that will allow you to edit both Word and Excel fies