I also am in the ACT. I think this is something that could be argued either way. If the units at the front are ‘class B’ units but the stack of units are ‘class A’ it might complicate how it might be argued. Still I think you could jump either way.
If a utility service is provided for the potential benefit of all units, facilities associated with the provision of that service are an Owners Corporation (OC) maintenance responsibility (UTMA s.24). So, it might be argued, the OC is providing an intercom service to all units and should fix any part of that service. If the OC wanted to go this way, it might pass a resolution declaring that it accepts that the provision, repair and maintenance of an intercom service to all units is an OC responsibility.
On the other hand, it could be argued that the individual intercoms on the separate units at the front of the complex are individually the responsibility of those individual units to repair and maintain. Each intercom is only providing a service to that one unit, a fact that remains unaltered by part of the device being on common property. The intercom on the ‘stack’ at the back, it could similarly be argued, does not service all units and is a responsibility of just the subset of units that are in the ‘stack’.
If the OC wanted to put it beyond doubt that it was an individual responsibility – just the ‘stack’ units share the cost of repair and maintenance of the stack intercom and the ‘front’ units are each responsible to fix their individual intercoms – the OC could pass a special resolution at a general meeting to that effect. It could be registered as an amendment to the OC rules. If anyone were to persist with an argument that it was an OC responsibility, the special resolution would also have satisfied the requirements of s.25 of the Act, whereby an OC may exempt itself from a maintenance responsibility by special resolution if it would not have a significant adverse effect on the appearance of the common property or the safety of occupiers of the units or the public.