1. A method for provisioning in a telecommunications network, the method comprising the steps of: receiving at least one request, from a requesting client system through an Application Program Interface, for defining measures relating to customers, services, or network elements in the telecommunications network; processing each request in functional layers of a provisioning system hosted by a network operator, where at least one functional layer includes independently mountable and dismountable functional modules; executing tasks in the telecommunications network according to the results of the processing step; and reporting the results to the requesting client system, wherein multiple telephone operators are allowed to use the provisioning system through an authenticated Application Program Interface, a Management User Interface, and an authorisation function module after provisioning rules are processed, where telephone operator's rights for use of network elements are controlled by the network operator, and the network operator is able to present and utilize one physical telecommunications network in many logical views, each view representing the network elements accessible to a telephone operator, and in this way controllable by the network operator with limitations, authentication and authorization rules.