The problem with the system I used is that is sent you a .tiff file or something like that. It was large and difficult to view. Also, sometimes I would get faxes that had a 1 year old fax still embedded in the attachment. It was really weird.
At work now, our copier acts as a scanner and is set up with our email addresses. We can scan a document to our email address and it comes in as a pdf file that can be forwarded or modified with the right program. That system works very well and I like it a lot. It works great for marking up drawings that have to be submitted with Management of Change paperwork. If you could find a service that used Acrobat files, that would be best IMHO.