Its not really necessary for them to have speech bubbles. You can make a script to refer to any dialogue. If you put speech bubbles in the story board it would annoy the both the actors (who need to know their lines) and the camera crew (who need to know their shots). A storyboard is to visualize the film and how the shots/ scenes may look when finished. If you do want to see how the dialogue will be, you can sort it out in the Animatic. The Animatic is essentially when you scan the storyboard into the computer and use the still images to ‘make’ a template of the movie. If there is any dialogue in scenes – you could record voices and put it in there. It would make more sense and help everybody a lot more.