A communication server for providing tariff information for a first communication device for calling a second communication device, the communication server comprising: a client interface with a first communication device; a network interface with a communication network; a processor, configured to: receive a client request for tariff information via the client interface, wherein the client request comprises an identity, ID, of the second communication device, transmit a network request for providing the tariff information via the network interface to the communication network, the network request comprising the ID of the second communication device, receive a network response to the network request via the network interface, the network response comprising the tariff information, wherein the tariff information indicates a tariff for the first communication device for calling the second communication device, and transmit the tariff information via the client interface to the first communication device, wherein the network request comprises a first network request directed to a porting database and a second network request directed to a customer relationship management, CRM, system, wherein the first network request is configured to request registry information of the second communication device; and wherein the second network request is configured to request the tariff information for the first communication device based on the registry information of the second communication device, wherein the network response comprises a first network response to the first network request, the first network response comprising a service provider ID associated with the ID of the second communication device, wherein the second network request comprises an ID of the first communication device and the service provider ID associated with the ID of the second communication device. a client interface with a first communication device; a network interface with a communication network; a processor, configured to: receive a client request for tariff information via the client interface, wherein the client request comprises an identity, ID, of the second communication device, transmit a network request for providing the tariff information via the network interface to the communication network, the network request comprising the ID of the second communication device, receive a network response to the network request via the network interface, the network response comprising the tariff information, wherein the tariff information indicates a tariff for the first communication device for calling the second communication device, and transmit the tariff information via the client interface to the first communication device, wherein the network request comprises a first network request directed to a porting database and a second network request directed to a customer relationship management, CRM, system, wherein the first network request is configured to request registry information of the second communication device; and wherein the second network request is configured to request the tariff information for the first communication device based on the registry information of the second communication device, wherein the network response comprises a first network response to the first network request, the first network response comprising a service provider ID associated with the ID of the second communication device, wherein the second network request comprises an ID of the first communication device and the service provider ID associated with the ID of the second communication device. receive a client request for tariff information via the client interface, wherein the client request comprises an identity, ID, of the second communication device, transmit a network request for providing the tariff information via the network interface to the communication network, the network request comprising the ID of the second communication device, receive a network response to the network request via the network interface, the network response comprising the tariff information, wherein the tariff information indicates a tariff for the first communication device for calling the second communication device, and transmit the tariff information via the client interface to the first communication device, wherein the network request comprises a first network request directed to a porting database and a second network request directed to a customer relationship management, CRM, system, wherein the first network request is configured to request registry information of the second communication device; and wherein the second network request is configured to request the tariff information for the first communication device based on the registry information of the second communication device, wherein the network response comprises a first network response to the first network request, the first network response comprising a service provider ID associated with the ID of the second communication device, wherein the second network request comprises an ID of the first communication device and the service provider ID associated with the ID of the second communication device.