Pros: It sends and receives faxes and makes coppies.
Cons: It has a printer port in the back USB. I hooked it up and Windows sees it as a HP 640c Printer using HP's online printer detection. When I called HP for support they told me there was no USB port in the back and hung up. Then the next guy explained that it won't print. Beautiful. So I'm going to try to see if Linux will auto detect the driver needed and print or do an lspci or lsusb.
Summary: The HP 640 is a simple to use fax machine. Very easy to set-up. Installing the ink cartridge is just like most ink-jet printers. Add paper, dial the number and press the button and you're on your way.
Cons: Comes with a ink cartridge that is "introductory", which means you get about 15 - 20 pages before it runs out of ink! Probably was something in the documentation about that, but when was the last time all of the documentation was read???