Establishing communication sessions

1. A method for establishing a communication session between a user in a telecommunications network and a remote party, the method comprising:

transmitting, at a communication session control system located in a signaling path for the communication session, a communication session establishment request, wherein the communication session establishment request includes a request to a given communication client, of a plurality of communication clients, to place the given communication client in a prior-to-answer session state, wherein the given communication client is on one of one or more user devices at which the user may accept the communication session establishment request and conduct voice communications with the remote party, and wherein the remote party is associated with a remote device;

receiving, in response to transmitting the communication session establishment request, a communication session hold response message from the given communication client, the communication session hold response message requesting that a communication session with the remote device be established initially in an on-hold state and that an option to retrieve the on-hold communication session be made available to at least one communication client of the plurality of communication clients other than the given communication client, wherein the at least one other communication client is on one of the one or more user devices at which the user may participate in the communication session;

determining, based on said communication session hold response message received from the given communication client, that the option to retrieve the on-hold communication session is to be made available to the at least one other communication clients; and

transmitting notification data to the at least one other communication client to notify the at least one other communication client that the on-hold communication session is available for retrieval by the at least one other communication client.

2. The method of claim 1 , further comprising:

receiving data identifying the at least one other communication client from the given communication client.

3. The method of claim 1 , further comprising:

determining that the communication session is to be established initially in the on-hold state; and

transmitting communication session setup data to allow the on-hold communication session to be established between the remote device and an intermediate node in the telecommunications network.

4. The method of claim 1 , wherein the intermediate node is the communication session control system.

5. The method of claim 3 , wherein media data is communicated via the on-hold communication session established between the remote device and the intermediate node to notify the remote party that the communication session has been established in the on-hold state.

6. The method of claim 5 , wherein at least some of the media data is selected from a set comprising a plurality of media data items.

7. The method of claim 5 , wherein data that identifies the media data is received from the given communication client.

8. The method of claim 5 , wherein the media data is selected on the basis of one or more predetermined media data selection rules.

9. The method of claim 5 , wherein the media data comprises video data.

10. The method of claim 1 , wherein the notification data is displayable on a graphical user interface.

11. The method of claim 1 , further comprising:

transmitting a communication session setup request to the at least one other communication client.

12. The method of claim 11 , further comprising:

receiving a communication session setup response from the at least one other communication client; and

causing a communication session to be established between the remote device and the at least one other communication client.

13. The method of claim 1 , wherein the given communication client and the least one other communication client are on different ones of the one or more user devices.

14. The method of claim 1 , wherein the given communication client and the at least one other communication client are co-located on one of the one or more user devices.

15. The method of claim 1 , wherein the notification data is configured to notify the at least one other communication client that the communication session is available for retrieval from the on-hold state.

16. The method of claim 15 , further comprising:

establishing a communication session with the at least one other communication client; and

connecting the communication session established with the remote device with the communication session established with the at least one other communication client.

17. The method of claim 1 , wherein the plurality of communication clients are associated with a client-shared telephony identifier.

18. The method of claim 1 , further comprising:

determining that the communication session is to be established initially in the on-hold state;

establishing a communication session with the remote device; and

applying a communication session hold treatment to the communication session.

19. A system for establishing a communication session between a user in a telecommunications network and a remote party, the system comprising:

one or more transmitters being locatable in a signaling path for the communication session and operable to transmit a communication session establishment request to a given communication client, of a plurality of communication clients, to place the given communication client in a prior-to-answer session state, wherein the given communication client is on one of one or more user devices at which the user may accept the communication session establishment request and conduct voice communications with the remote party, and wherein the remote party is associated with a remote device; and

one or more receivers operable to receive, in response to transmitting the communication session establishment request, a communication session hold response message from the given communication client, the communication session hold response message requesting that the communication session with the remote device be established initially in an on-hold state and that an option to retrieve the on-hold communication session be made available to at least one communication client of the plurality of communication clients other than the given communication client, wherein the at least one other communication client is on one of the one or more user devices at which the user may participate in the communication session,

wherein the system is configured to determine, based on said communication session hold response message received from the given communication client, that the option to retrieve the on-hold communication session is to be made available to the at least one other communication client, and wherein said system further comprises:

one or more transmitters operable to transmit notification data to the at least one other communication client to notify the at least one other communication client that the on-hold communication session is available for retrieval by the at least one other communication client.

20. A non-transitory computer-readable storage medium comprising computer-executable instructions which, when executed by a processor, cause a computerized device to perform a method for establishing a communication session between a user in a telecommunications network and a remote party, the method comprising:

transmitting, at a communication session control system located in a signaling path for the communication session, a communication session establishment request, wherein the communication session establishment request includes a request to a given communication client, of a plurality of communication clients, to place the given communication client in a prior-to-answer session state, the given communication client is on one of one or more user devices at which the user may accept the communication session establishment request and conduct voice communications with the remote party, wherein the remote party is associated with a remote device;

receiving, in response to transmitting the communication session establishment request, a communication session hold response message from the given communication client, the communication session hold response message requesting that the communication session with the remote device be established initially in an on-hold state and that an option to retrieve the on-hold communication session be made available to at least one communication client of the plurality of communication clients other than the given communication client, wherein the at least one other communication client is on one of the one or more user devices at which the user may participate in the communication session;

determining, based on said communication session hold response message received from the given communication client, that the option to retrieve the on-hold communication session is to be made available to the at least one other communication client; and

transmitting notification data to the at least one other communication client to notify the at least one other communication client that the on-hold communication session is available for retrieval by the at least one other communication client.