The Targus PA560U is a CF 56K V.90 modem with a 56.6Kbps data and 14.4Kbps fax transfer rate. It is 88mm x 42.8mm x 6.3mm (or 3.5in L x 1.7in W x 0.25in H), and so it sticks a couple of inches out of the Z. This is a little annoying, but bearable. The card seems to suck less power (so doesn't run down the battery as fast) and gets a faster connection than via WiFi, so even though you are less mobile it is a good idea if you have easy access to a jack. The card has a pop-up connection for the phone line, and is rated at 0.2W when active.
Go into Network Setup, Choose Dial-up-PPP, Click on New, highlight Dial-up-PPP and click on add, and then fill out the information in the various tabs.
Then all you have to do is click on the globe icon with a red X on it, and the modem will get initialized, it will dial out and get authenticated. Once you're logged in you can use e-mail or browse using Netfront (below...).