Eastern Australia? Where exactly? (No, I'm not one of those odd criminals..it's just that I simply love your country!).
Back to your question. I'm not a telco expert so, waiting for some expert to better reply, here it is my thinking aloud attempt.
Since I am quite sure you don't run your own cell tower, I think you have no way to know which mobiles are bound to the nearest cell to your property.
A smart, unreliable way could be to activate an open wi-fi access point. That way, if an intruder has its wifi on, it is possible that his device ping your access point; in that case you'll be alerted of incoming devices.
Another way could be to place IR devices around electro/telco facilities. They will constitute sort of an electronic fence, able to alert you when someone pass-through its rays (could be technicians, animals..).
You could even "sell" the idea to those companies as a way to secure their facilities.
A final point, I don't know how it's ruled in Australia but in other countries companies gain a right to enter at any time a private property (right of way/easement) if that's the path to their facilities; more so if the facilities are placed inside your property.
Update:
@BillMeyer WOW, sounds great!
udg