Do parts of Australia still use the differently phased power grid?
I think it used the ground as the return?
Sorry if it's a bit old here mate, but that's an good & understandable question!

Here in Australia, we transmit power at many varying voltages, depending on the distance. Ranging from 275-kv,
right down to typically 11-kv into the Suburbs. All this is via 3-Phase
Delta. Usually, the final legs in our typical
streets is 11-kv (Delta) to 415v (
Star connections), and so producing a virtual 'neutral' at the star-point. The result
of this is to create 240v from each phase to the star-point, being the common 'Neutral'. You will find in the typical street,
that every 3rd or 4th house is connected to varying phases, including the common star-point. Even though this is so, our
switchboards have a main earth, as well as a link from the main earth bar to the neutral bar. We call this a
M.E.N. link,
which means Mains-Earth-Neutral. Now partially answering your question....
In some typically remote Country/Farm locations, there is a system known as
S.W.E.R., which stands for 'Single Wire
Earth Return'. For that, there is a typically 9.6kv single wire transmission through the majority of the transmission, where
at the farms etc, has a 9.6kv to 415v/240v transformer, where the 'HV' uses Earth as the return! (Reduced cabling!)

Interesting addendum....
Different countries use different HV transmission voltages. This is mainly due to to countries local cost for copper/aluminium
as opposed to cost of towers/insulators etc!! Although the higher 'HV' seems better, the local cost is a different story!!