A system can be, and often is, a personal ordering of reality, the result of seeing some degree of orderly interconnectedness in some part of the world. So a system can be many different kinds of system simultaneously, depending on who is studying it and why. Different viewpoints of a system correspond to different sets of users and therefore different purposes. In this sense, it is a subjective ordering of reality.
A telephone system is a communications system to its users. For the engineers who set it up and maintain it, it is a technical system (that is linked to an employment system – a job – in their view). Similarly someone who designs telephone switches considers each switch as a system in its own right – a switch can record usage data as well as route your calls.
As Example 3 shows, there is a notion of what is included within a system, and what is excluded. Naturally this notion depends on the stakeholders involved in the modelling and development of the system and the viewpoints that they have over it. Identifying the scope of a system is an essential step in the development process.