LG LGMS840 - Manual (Page 109)

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Communication
To chat on or off-the-record
Your Google Talk messages are stored, so you can review them later and
even search for them, in the Chats folder in Gmail. If you’d rather not store
the messages in a chat, you can chat off-the-record.
 While chatting, touch the Menu Key > Chat off record.
To return to on-the-record chatting, touch the Menu Key > Chat
on record.
To end a chat
When you’ve finished your conversation, it’s easy to end a chat session.
 From your Friends list, touch and hold the friend you want to stop
chatting with. In the Context menu that opens, touch End chat.
OR
 From a chat screen, touch the Menu Key > End chat.