"Also, it's my understanding that {shippin'} is really {shippen} -- that is,
a remnant of a dialect that generalized a different form, so there is no {g}
to be dropped." I K PEYLOUGH, SOUTH FLORIDA

Sorry, I am quite at sea here.

I have often heard English people pronounce the verbal ending -ing [In] or
even [@n] : dancing > dancin' etc., and I thought this form what just
regarded as colloquial.

If they didn't drop a /g/, what would make them replace /N/ by /n/?

Jean-Paul G. POTET, FRANCE