The invention is a method and apparatus for on-demand resource planning for unified messaging services. In one embodiment, multiple clients are served by a single system, and existing system resources are allocated among all clients in a manner that optimizes system output and service provider profit without the need to increase system resources. In one embodiment, resource allocation and job scheduling are guided by individual service level agreements between the service provider and the clients that dictate minimum service levels that must be achieved by the system. Jobs are processed in a manner that at least meets the specified service levels, and the benefit or profit derived by the service provider is maximized by prioritizing incoming job requests within the parameters of the specified service levels while meeting the specified service levels. Thus, operation and hardware costs remain substantially unchanged, while system output and profit are maximized.