Samsung M520 Owner's Manual page 44

Indicates that you have new voicemail, text, numeric pages,
picture messages, video messages, or Wireless Application
Protocol (WAP) messages waiting.
Indicates that there is an unread message in your Inbox.
Indicates that the text message has been read.
Indicates that there is an unread urgent message in your Inbox.
Indicates that you have read the urgent message.
Indicates that the message was sent.
X
Indicates that the message failed to be sent.
Indicates that you have a message pending.
Indicates that the message is a draft.
Indicates that there is URL text contained within the text
message.
Indicates that your message is locked.
Indicates that your phone is in vibrate all mode.
Indicates that your phone ringer is turned on and the vibrate
mode option is checked.
Indicates that the TTY option is on.
Indicates that the ringer is set at a level between 1 - 8 or
that 1-Beep is selected.
Indicates that your phone's ringer is turned off and the vibrate
mode is not checked.
Indicates that an alarm is set on your phone.
Indicates your phone is in use and a call is in progress.
18 Section 2A: Phone Basics