Samsung SPH-M300 User Manual page 238

When is my data connection dormant?
If no data is received for 10 seconds, the connection goes
dormant. When the connection is dormant, voice calls are
allowed. (The connection may become active again quickly.) If
no data is received for an extended period of time, the
connection will terminate.
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 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 > Data > Off Data in your phone's menu.
214 Section 3B: Sprint Vision