A method for providing a service in a telecommunications network comprising a plurality of resources and at least one slice of resources. The method comprises actions of receiving, creating and modifying. A request is received from a customer to serve a group of user devices by a first service. A new NSI is created to provide the first service, if it is determined that there is no existing NSI, shareable between a plurality of services, that can provide the first service. An existing NSI, shareable between a plurality of services, is modified to serve the group of user devices by that first service in addition to at least one second service that is already provided by the existing NSI, if it is determined that the existing NSI can provide the first service.