King David's Magic 8 Ball

So, since we're reading through the bible in a year, both my wife an I are in 2 Samuel. This weekend, we were discussing the use and purpose of the ephod. The ephod, at face value, was a piece of clothing, but not a complete outfit in itself. It is usally described in the bible as being worn, and is often mentioned as being linen. However, in the story linked above, and later in others, King David is seen consulting the ephod like it's some kind of Magic 8-Ball. I almost expect the conversation to go like this:

David: Should I attack the Philistines
Ephod: All signs point to yes
David: (Leaves to attack the Philistines)

David: Should I kill King Saul?
Ephod: Ask again later
David: (Cuts section from Saul's robe)

Does anyone have any insight into the ephod? How about the Urim and Thummim, which appeared to be a part of the breastplate, and which Saul used to help discern God's will?

Just one of the mysteries I may have to wait for heaven to learn....