well u can use messenger discovery and use a thing call offline talking. it will mean u have to block all your contacts tho, thus they won't be able to start chats with u as u as u appear offline, but u can start chats with them
http://www.messengerdiscovery.com
i think stuffplug-NG has a feature simular to this too, but no sure on that on
http://www.stuffplug.com