One can always take a photograph of the document using the iphone and email it straight from the iPhone. That should, atleast in some cases, as good as fax. The recipient can print the email attachment.
I have tried this a couple of times with success. The main problem is getting the document to line up properly, the angle of holding the iphone and the placement of the documetn on a flat surface. If the document has folds in it, that is another challenge.
Here is an opportunity for an iPhone app, a limited functionality image processing app, to clean up the photographed document before emailing.