Samsung SPHM500 Service Manual page 228

Can I sign out of data services?
You can sign out without turning off your phone; however, you will not be
able to browse the Web or use other Sprint PCS Vision services. While
signed out, you can still place or receive phone calls, check voicemail, and
use other voice services. You may sign in again at any time. To sign out, go
to Settings > Power Vision > Disable Vision in your phone's menu.
204 Section 3B: Sprint PCS Vision