Samsung M520 Owner's Manual page 246

Sprint Vision Connection Status and Indicators
Your phone's display lets you know the current status of your Sprint Vision
connection through indicators which appear at the top of the screen. The
following symbols are used:
If no indicator appears, your phone does not have a current Sprint Vision or
Sprint Power Vision connection. To launch a connection, see "Launching a
Sprint Vision Connection" on page 218.
220 Section 3B: Sprint Vision
Your Sprint Vision connection is active (data is being
transferred); the transmit/receive symbol will blink to indicate
data transmission. Incoming voice calls go directly to voicemail;
outgoing voice calls can be made, but the Sprint Vision
connection will terminate.
Your Sprint Vision connection is dormant (no data is being sent
or received). Though not currently active, when dormant the
phone can restart an active connection quickly; voice calls can
be made and received.
Your phone is not currently able to access Sprint Vision service
features.
Your phone is connected to a high-speed Sprint Power Vision
connection.
A high-speed Sprint Power Vision connection is available.
The high-speed Sprint Power Vision connection is dormant.
Your high-speed Sprint Power Vision connection is active.