The airport I work at is approximately 200 miles from the oceanic entry point, therefore aircraft departing here are issued their oceanic clearance prior to take off. It would generally read something like
SID KOBEV 50/50 51/40 51/30 52/20 LIMRI XETBO EXPECT FL330 M .80 DEPART RWY AND SQUAWK.
Aircraft departing from other points would get their oceanic clearance from Ocean Clearance Delivery while still in domestic airspace.
I don't recall anyone ever going across without an oceanic clearance due to a comm failure, which means it will probably happen during my next shift...
Tc