I don't know of a tutorial on this. I would suggest creating a gui theme, and modifying the panel or some other component that can deal with 9 slice textures. You then design your 9 slice to look like a speech bubble. Once this has been done, you could could add a label node as a child of your panel.. then have a script on your panel ensure that the panel increases decreases its size to match the size of the label.. does that help?
