In the field of telecommunication, a service may be employed for providing access to multiple subscribers by means of a single telephone number. This service is useful when a calling party wishes to access a certain group of subscribers with certain characteristics in common, without having to look up and dial the phone number of every subscriber. Instead, a “virtual” phone number representing the group can be conveniently used such that whenever a person dials the virtual phone number on his/her communication device, hereafter referred to as a “caller” for short, the subscribers will be called “iteratively”, i.e. one by one according to a calling list or the like. For example, a sales person may wish to call potential customers living within a certain area for offering services or products which may be deemed particularly attractive for specific customers. However, the current technique is not capable of protecting privacy and integrity in a satisfactory way.