An aerial installation is where the cable is hung from an electricity pole to the house. A TOW authorises Dig Dug to supply and install this cable.
Most new houses in the ACT have underground installations as many ACTPLA approvals require the electricity to be underground - so utilising the same trench costs no extra.
Dig Dug can also quote you privately to supply the trench. Telstra do not provide trenches inside the customers boundary.