Shoutbox

I'm guessing by Offline Talker that you mean being able to talk to your contact while your status to them is offline

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You can download the Stuffplug NG plugin

Once installed, to enable Offline Talking, go to:

Plus! > Preferences > Plugins > Stuffplug NG > Configure > Conversations > Enable Allow talking to blocked contacts

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Or you could download the Messenger Discovery X addon

You can enable the feature Invisible Talking

Heres a screenshot: Invisible Talking

Both of these programs allow you to talk to your contacts while your status to them is offline