A method performed by a call-tracking system, comprising the steps of - inserting in a request for a web page to a web server host from a first user equipment associated with a first telephone number, an information header with data indicating to the web server host that possible calls from the first user equipment can be tracked by the call-tracking system, - forwarding the request to the web server host; - receiving in response to the request, a reply message comprising the web page and at least one second telephone number associated with a second user equipment and an HTTP header comprising the second telephone number; - forwarding the reply message to the first user equipment; - retrieving the first telephone number, the second telephone number, a time associated with the forwarding of the reply message to the first user equipment, and a service provider indicator for a service provider associated with the web server host, e.g. a URL of the service provider; - storing, associated with each other in a first database, the first telephone number, the second telephone number, the service provider indicator and the time associated with the forwarding of the reply message; - receiving from a proxy server a trigger message comprising two telephone numbers, said trigger message indicating a telephone call related to the two telephone numbers; - determining whether the two telephone numbers correspond to the first telephone number and the second telephone number stored associated with each other in the first database; - if the two telephone numbers correspond to the first telephone number and the second telephone number, determining, based on a time difference between the time associated with the forwarding of the reply message and a time indicative of when the telephone call was made, whether the call has been made within a predetermined time or predetermined time interval from the forwarding of the reply message; and, - if the call has been made within the predetermined time or predetermined time interval, store information related to the call in the first database or a second database. - inserting in a request for a web page to a web server host from a first user equipment associated with a first telephone number, an information header with data indicating to the web server host that possible calls from the first user equipment can be tracked by the call-tracking system, - forwarding the request to the web server host; - receiving in response to the request, a reply message comprising the web page and at least one second telephone number associated with a second user equipment and an HTTP header comprising the second telephone number; - forwarding the reply message to the first user equipment; - retrieving the first telephone number, the second telephone number, a time associated with the forwarding of the reply message to the first user equipment, and a service provider indicator for a service provider associated with the web server host, e.g. a URL of the service provider; - storing, associated with each other in a first database, the first telephone number, the second telephone number, the service provider indicator and the time associated with the forwarding of the reply message; - receiving from a proxy server a trigger message comprising two telephone numbers, said trigger message indicating a telephone call related to the two telephone numbers; - determining whether the two telephone numbers correspond to the first telephone number and the second telephone number stored associated with each other in the first database; - if the two telephone numbers correspond to the first telephone number and the second telephone number, determining, based on a time difference between the time associated with the forwarding of the reply message and a time indicative of when the telephone call was made, whether the call has been made within a predetermined time or predetermined time interval from the forwarding of the reply message; and, - if the call has been made within the predetermined time or predetermined time interval, store information related to the call in the first database or a second database.