What's so hard about eliminating all the air above a saucer?
Just think for a moment how fast your flying saucer would go if you had no air pressing down on it. You just have to be careful not to open the top hatch while saucering.
On another note, the communicators used by the mid-22nd century crew of United Planets Cruiser C-57D in Forbidden Planet were better than the ones used by Jim Kirk's crew: they had video capability and were not likely to be lost.