Controlling communications

1. A gateway associated with a first network having one or more first end-user computer terminals and one or more corresponding telephone units, the gateway to enable communication with a second, packet-based network comprising one or more second end-user computer terminals installed with a communication client of the second network, the one or more telephone units for performing calls with one of the second end-user computer terminals over the second network the gateway comprising:

a switching apparatus including a processing device and a gateway engine operable via the processing device and configured to:

automatically detect in association with a call whether a user operates one of said first end-user computer terminals or uses one of said telephone units to select respectively between a first state in which the call is to be performed using one of said first end-user computer terminals and a second state in which the call is to be performed using one of said telephone units; and

route the call based on the selection between the first state and the second state including:

on condition of detecting user operation of one of said first end-user computer terminals, selecting the first state and routing both call set-up signalling and call media to the first end-user computer terminal; and

on condition of detecting use of one of said telephone units, selecting the second state routing call set-up signalling to the first end-user terminal, and routing the call media to the one of said telephone units.

2. The gateway of claim 1 , wherein the switching apparatus is configured to perform selection of the state by detecting at least one of: in the case of an incoming call, whether a user answers the incoming call using the first end-user computer terminal or the phone units; and in the case of an outgoing call, whether the user initiates the outgoing call using the first end-user computer terminal or the phone unit.

3. The gateway of claim 1 , wherein the switching apparatus is configured to perform said detection by receiving at least one of a signal and an absence of a signal from the first end-user computer terminal.

4. The gateway of claim 1 , wherein the communication client of the first end-user computer terminal is configured, if the second state is selected, to transmit a call control signal to the phone unit in order to control the call.

5. The gateway of claim 1 , wherein the switching apparatus comprises a signal processing device configured, if the second state is selected, to decode call media received from the second end-user computer terminal over the second network for routing to the telephone unit.

6. The gateway of claim 1 , wherein the switching apparatus comprises a signal processing device configured, if the second state is selected, to encode call media received from the telephone unit for transmission to the second end-user computer terminal over the second network.

7. The gateway of claim 1 , wherein the switching apparatus comprises a signal processing device configured, if the second state is selected, to transcode call media transmitted between the telephone unit and the second end-user computer terminal.

8. The gateway of claim 1 , wherein at least one of the gateway and the client on the first end-user computer terminal is configured to negotiate a codec for said call media that is common to the second end-user computer terminal and at least one of the phone unit and the first end-user computer terminal.

9. The gateway of claim 8 , wherein the negotiation comprises determining a common subset of codecs, then selecting a codec from said common subset.

10. The gateway of claim 1 , wherein the switching apparatus comprises a signal processing device configured, if the second state is selected, to decrypt call media received from the second end-user computer terminal over the second network for routing to the telephone unit.

11. The gateway of claim 10 , wherein the switching apparatus is arranged to receive and store a decryption key of the second end-user computer terminal for use in decrypting said call media.

12. The gateway of claim 1 , wherein the switching apparatus comprises a signal processing device configured, if the second state is selected, to encrypt call media received from the telephone unit for transmission to the second end-user computer terminal over the second network.

13. The gateway of claim 1 , wherein the telephone unit is a wired telephone unit.

14. The gateway of claim 1 , wherein the first network is a private network and second network is a public network.

15. The gateway of claim 1 , wherein the call set-up signalling includes at least a call request message.

16. The gateway of claim 1 , wherein the call set-up signalling includes at least an authentication procedure.

17. The gateway of claim 16 , wherein the communication clients are peer-to-peer clients and the authentication comprises exchange of peer-to-peer authentication certificates.

18. The gateway of claim 1 , wherein the first network comprises: a packet-based network portion comprising said one or more first end-user computer terminals and said gateway, and a branch exchange portion comprising said one or more telephone units.

19. A method for use in a first network comprising one or more first end-user computer terminals, a gateway to a second packet-based network comprising one or more second end-user computer terminals installed with a communication client of the second network, and one or more telephone units for performing calls with one of the second end-user computer terminals over the second network; the method comprising:

detecting at the gateway a signal that indicates whether a user operates one of said first end-user computer terminals or uses one of said telephone units for a call, the signal employed by the gateway to make a selection between a first state in which one of said calls is to be performed using one of said first end-user computer terminals and a second state in which the call is to be performed using one of said telephone units; and

on condition of detecting the first state, routing by the gateway both call set-up signalling and call media to the first end-user computer terminal; and

on condition of detecting the second state, routing by the gateway call set-up signalling to the first end-user terminal and routing the call media to the one of said telephone unit.

20. A computer program product for a gateway connected to one or more first end-user computer terminals, in a first network to enable communication with a second packet-based network comprising one or more second end-user computer terminals installed with a communication client of the second network, and one or more telephone units for performing calls with one of the second end-user computer terminals over the second network, wherein each of the one or more first end-user terminals is installed with a communication client for performing calls with the second end-user computer terminals over the second network; the program product comprising code embodied on a computer readable storage device connected to the gateway and configured so as when executed on the gateway to:

select a first state in which one of said calls is to be performed using one of said first end-user computer terminals or a second state in which the call is to be performed using one of said telephone units based upon automatic determination of whether or not a telephone unit is used for the call; and

apply pairing to pair the telephone unit with the gateway dependent upon the determination including:

on condition of selecting the first state, foregoing the pairing and routing both call set-up signalling and call media to the first end-user computer terminal; and

on condition of selecting the second state, applying the pairing, routing call set-up signalling to the first end-user terminal and routing the call media to the one of said telephone units.