I seem to be in a bit of a BGA mood lately. I do that sometimes - pick a subject and talk it to death before moving on. Well, maybe not quite talk it to death, but at least talk it to the pain.
Take a look at this land pattern for a bluetooth module. Anyone see anything odd? Yeah. All of those really big open vias. I know what the designer was trying to do. A good number of the vias are ground connections of one sort or another that need to be connected to an internal ground plane layer.
Given that is is a 1mm pitch BGA, there is plenty of room to put the vias between the pads and not cause any trouble. That would be one recommended approach. The other would be to have the vias filled and plated over at the board house. No matter what you do, though, the vias can't be left wide open like this. It's a real bummer.
B.V.O.U.S.'s? BGA Vias Of Unusual Size. I don't think they exist.