Originally Posted by
Dick Smith
In the USA, most pilots on an IFR flight plan take off and climb through E without a clearance to 17,500 feet when VMC exists
I'm not sure I understand the question. I am pretty sure in the situation you describe, the pilots will be operating under visual flight rules until they have their IFR clearance i.e. despite the flight plan they are VFR. And the opposite seems pretty common on approach, cancelling IFR once they are visual and no longer need IFR-IFR separation by ATC.
I don't know if there is a procedure to change from VFR to IFR in the air in Australia - it seems like it must be possible?