To respond to messages you receive
If you’re working in a message window, messages that you receive
from that contact are displayed. Otherwise, you receive a new message
notification and a new message icon 
appears in the Status Bar.
When you tap the new message notification, the Message screen opens
where you can reply to the message.
NOTE
The message pop-up box appears on any screen so that you can instantly reply to the message without closing the application.
If the Auto-retrieve setting is not checkmarked, you must tap the Download button to view the message.
If the message contains a media file, tap the Play button to view, watch, or listen to it. Touch and hold the media file to open a Context menu with additional options.