Microsoft Office 2003 lets users send faxes directly from within the application suite, after registering with an internet fax provider. Here's how they describe it on their website:
Fax Through the Internet, Not Your Modem
Integrated Internet faxing in Outlook 2003 enables you to send faxes using features a typical fax machine doesn't offer. For example, use fax numbers in Contacts, use the preview tool to view a fax before sending it, calculate the cost of the fax before sending it, add cover pages that you can modify in Microsoft Office Word 2003, or sign your name on the fax using a Tablet PC. You can also receive faxes in your Inbox.