Interesting point, but if the masseuse realized something was wrong, 911 should have been the first call...and a relatively quick call, at that. I think life and death transcends any type of code.
Obviously, though, we don't know exactly what the masseuse (hereby referred to as the girl) did to try to wake him or if Ledger was still breathing at the time the girl arrived. If he was still breathing, then perhaps the girl didn't grasp the immediacy of the situation.
It probably was a touchy situation for the girl, too. With the way celebrities are treated, it is reasonable to think that the girl didn't go to great lengths to wake him up for fear of making him mad or whatever.