You can but it for $24.99, but they also have a 15 day demo so you can try before you buy. According to Navizon the WiFi GPS system works like this: "...people with a GPS device collect the location information of cell towers and wifi access points. Then they share it with the rest of the network and everyone else who doesn't have a GPS device can then simulate a Virtual GPS thanks to the data collected by others. This is why we call it Peer to Peer positioning."

Looks like the easiest way to install the application on your iPhone is to use the Installer.app. Takes about 30 seconds to get your location within a few hundred yards, which is good enough to get directions from your current location with Google Maps. More info is available at Navizon's website.