This software allows you to transform the data plan on your Windows Mobile based smart phone (here is a list of compatible phones) into a WiFi router for less than a one time $30 fee.
I find this solution most useful for when you have an unlimited data plan and you have several devices such as a iPod Touch and a NetBook that only have WiFi access.
Be sure to check with your cell phone provider to make sure you are not violating any terms of use.