Method for providing subscriptions to packet-switched networks

1. A method for providing a subscription to an IP Internet-Protocol based Multimedia Subsystem (IMS) for a first client of a packet-switched network, the method comprising:

a) identifying the first client by a Mobile Subscriber Integrated Services Digital Network (MSISDN) number, and identifying a second, mobile client of a circuit-switched network by a MSISDN number that is identical to the MSISDN number identifying the first client;

b) sending, by the first client, a register request to an IMS Server via the packet-switched network;

c) sending, by the IMS server, a location query request to a Home Subscriber Server (HSS) register;

d) requesting, by the HSS register, user subscription information of the circuit-switched network from a Home Location Register (HLR) of the circuit switched network;

e) sending, by the HLR of the circuit-switched network, to the HSS register, the user subscription information of the second client; and

f) creating, by the HSS register, a user IMS subscription information based on the user subscription information received in step e).

2. The method according to claim 1 , wherein the method further comprises:

f) sending, by the HSS register, authorization information to the IMS server; and

g) sending, by the IMS server, an authorization challenge to the first client.

3. The method according to claim 1 , wherein in step b) the request includes a Internet-Protocol Multimedia Private Identity (IMPI) and a temporary Internet-Protocol Multimedia Public Identity (IMPU) which is generated from an International Mobile Subscriber Identity (IMSI) of the second client.

4. The method according to claim 3 , wherein in step e) a new Internet-Protocol Multimedia Public Identity (IMPU) is generated based on the MSISDN of the first client and the second client.

5. The method according to claim 1 , wherein in step a) the request is sent to a Proxy Call Session Control Function (CSCF) and in step b) the location query request is sent by an Interrogation Call Session Control Function (CSCF).

6. The method according to claim 1 , wherein the circuit-switched network is an wireless telephony network.

7. The method according to claim 1 , wherein the first client and the second client are incorporated in one device.

8. The method according to claim 1 , wherein, after creation of the user identity of the IMS network, the authentication of the first client is done according to an IMS Authentication and Authorization (AKA) Agreement procedures.

9. A server for storing user identities of an Internet-Protocol Multimedia Subsystem (IMS) network, the server comprising: a Home Subscriber Server (HSS) register for storing IMS user identities for an IMS network;

a receiver unit for receiving requests for IMS user identities;

a transfer unit that requests user data of an circuit-switched network from a Home Location Register (HLR) of the circuit-switched network, if the receiver unit receives an request for an IMS user identity that is not stored in the HSS register; and

a creation unit to generate the IMS user identity based on the user data received from the HLR of the circuit-switched network.

10. The server according to claim 9 , wherein the creation unit generates a new Internet-Protocol Multimedia Public Identity (IMPU) based on a Mobile Subscriber Integrated Services Digital Network (MSISDN) number of the first client and a MSISDN number of a second client.

11. The server according to claim 9 , further comprising a sender unit which sends the IMS user identity, which was generated by the creation unit, to an IMS server.