Y was my friend appear offline in facebook?

[Jet]

some of my friend appear offline in my facebook(they does not have greenlight beside their name,but there was a phone) althrough they was online
I ask them that wat is my situation on their chatbox,they say it is appear offline too(no greenlight)
How can i solve tis problem?????Pls help me

[joker]

Theres a little gear somewhere next to the chat, it should be turned on so you're online.

[Jess]

If it has a phone next to their name it means that they are signed in on a mobile device like an iPhone, iPod or Blackberry. If you send them a message in their chat back it will go to their personal inbox. This is because most of the Facebook apps for mobiles don't support the chat features. They will still be online, but they will have to talk to you through inbox.

[Daniel]

You Cant Solve the Problem The Mobile Phone Sign Means they Are Online on there Mobile Device your Facebook Chat is Working Fine

[Jeanne]

I think they have turn off the chat.