Well, the developers of Pamela Calls Recorder (an add-in for recording Skype calls) have released a Skype plugin called PamFax that lets you send and receive fax documents from your computer to any number (fax machine) in the world though Skype.
You type in the facsimile number of the recipient (who uses a real fax machine, not Skype), select the document file, a fax cover sheet and hit send. You can chose to receive fax delivery confirmation via Skype chat or in your email inbox.
Also see: Use Google Docs for Sending Online Fax
In Windows Explorer, you can fax any supported document from the context menu of the file. A PamFax toolbar button is added to Microsoft Office to directly fax the current document from Microsoft Word or Microsoft Excel.
Unlike the free Fax via Email services, PamFax would require to pay via Skype Credits which can be linked to your PayPal account. Fax rates per page vary between € 0.17 and € 1.59 depending on the country of the recipient. There are however no subscriptions or monthly fees.