An application I was working on recently required the ability to send a fax of a PDF. I have done fax integration in the past using Brooktrout hardware and FacSYS and other servers. I must admit not only was I dreading doing the integration I worried that the client would balk at the startup cost.
Then I came across Interfax. This is a faxing Web Service! Reasonable at .07/page for nationwide faxing.
Check them out.