Green’s Dictionary of Slang

1. a blow, esp. with the fist [post-1930s use is mainly Aus.].

1941		Baker Popular Dict. Aus. Sl. 24: Dong, a blow, esp. with the fist.
1965		(con. 1940s) N. Hilliard Power of Joy 223: ‘Ten dongs!’ [...] The usual punishment was six dongs but this was a serious case.
1965		Teleg. (Brisbane) 5 July 8: Dong, poke (punch) [OED].
1983		J. Byrell (con. 1959) Up the Cross 92: [He[ gave the baddies another couple of dongs apiece for good measure.
1996		J. Byrell Lairs, Urgers & Coat-Tuggers 74: [I]t looked like Big Oscar might cop a dong on the nut.

2. a phonecall, a ring.

1997

‘Q’ Deadmeat 118: I’ll give him a dong on his moby.