From the FAQs:
http://navigation.sprint.com/planreq.html
Q: How do I find/purchase Sprint Navigation?
A: Sprint users must subscribe to a data plan in order to use Sprint Navigation. If you already have a data plan, click here to learn how to download Sprint Navigation.
If you do not already have a data plan, you can sign up for one by doing one of the following:
* Go to the
www.sprint.com and sign in to "My Sprint Wireless" to upgrade to a Power Vision Data Plan that includes Navigation
* Call 1-800-SPRINT1 to upgrade to a Power Vision Data Plan or purchase Sprint Navigation for $9.99/month *
* Go to a store and ask to upgrade to a Power Vision Data Plan or purchase Sprint Navigation for $9.99/month *
*Note: Without a data plan, Sprint Navigation will incur data usage costs.