John: I don't think the free for all ATM system would work, in fact, it would be a disadvantage to the larger institutions. The "Big 3" as they're now known have substantially more customers than say a credit union or the likes of Suncorp, Bank of Queensland etc. To provide these atm's comes at a cost of rental for the equipment, rental on the premises, servicing charges, security & reporting expenses plus no doubt a number of other expenses.
Why should the larger banks subsidise the smaller ones because they lack the infrastructure?
If you want to feel all warm and fuzzy about being a member and banks not charging fees, perhaps a credit union or building society is more suitable. While these smaller players appear to be "cheaper" they lack the ability to provide the infrastructure; number of atms, sms banking, easy to use internet banking platforms, branches etc - Then they don't necessarily compete on price in regards to lending products.