Processing communication sessions

1. A method of moving an established communication session in a telecommunications network, the communication session being established between a first device in a plurality of user devices associated with a user and a remote user device associated with a remote party, to a second device in the plurality of user devices associated with the user, the method comprising:

at the second user device, transmitting a request to a SIP registrar entity in the network to be notified of registration of user devices in the plurality with the network;

at the second user device, in response to the transmittal of the request to the SIP registrar entity, receiving a message from the SIP registrar entity indicating that the first user device has registered with the network, the message received from the SIP registrar entity comprising contact information for the first user device;

at the second user device, transmitting a request to the first user device to be notified of any communication sessions established with the first user device, wherein the request transmitted to the first user device is transmitted using the contact information for the first user device received from the SIP registrar entity;

at the second user device, receiving, from the first user device, a message indicating that a communication session has been established between the first user device and the remote user device, the message comprising contact information for the remote user device, wherein the message indicating that a communication session has been established between the first user device and the remote user device is received in response to the transmittal of the request to the first user device;

at the second user device, in response to receipt of the message indicating that a communication session has been established between the first user device and the remote user device, configuring a user interface on the second user device to display a call pull option;

at the second user device, receiving user input via the call pull option displayed on the second user device; and

at the second user device, in response to the user input via the call pull option displayed on the second user device, transmitting, to the remote user device using the contact information comprised in the message, a request to replace the communication session established between the first user device and the remote user device with a communication session between the second user device and the remote user device.

2. A method according to claim 1 , wherein the message further comprises an identifier for the communication session established between the first user device and the remote user device, and

wherein the request transmitted to the remote user device comprises the identifier.

3. A method according to claim 1 , wherein the request transmitted to the first user device comprises a SIP SUBSCRIBE (Event=dialog) message or a SIP INFO message.

4. A method according to claim 1 , wherein the request transmitted to the SIP registrar entity comprises a SIP SUBSCRIBE (Event=reg) message or a SIP INFO message.

5. A method according to claim 1 , comprising, prior to transmittal of the request to be notified of registration of user devices to the SIP registrar entity, transmitting a registration request for the second user device to a SIP registrar entity in the network, the registration request comprising contact information for the second user device.

6. A method according to claim 1 , wherein the request transmitted to the first user device is transmitted to the first user device without passing via an application server entity in the network.

7. A method according to claim 1 , wherein the request transmitted to the remote party device comprises a SIP INVITE (Replaces) message.

8. A method according to claim 2 , wherein the identifier for the communication session is comprised in a SIP Replaces header in the SIP INVITE (Replaces) message and comprises a SIP dialog identifier for the communication session established between the first user device and the remote user device.

9. A method according to claim 1 , wherein the message indicating that the first user device has registered with the network comprises a SIP NOTIFY (Event=reg) message or a SIP INFO message.

10. A method according to claim 1 , wherein the message indicating that a communication session has been established comprises a SIP NOTIFY (Event=dialog) message or a SIP INFO message.

11. A method according to claim 1 , comprising receiving, from the remote user device, an indication that the request to establish a communication session with the remote user device has been accepted.

12. A method according to claim 11 , wherein the acceptance indication received from the remote user device comprises a SIP 200 OK message.

13. A method according to claim 1 , wherein the moving comprises a call pull operation from the first user device to the second user device.

14. Apparatus for use in moving an established communication session in a telecommunications network, the communication session being established between a first device in a plurality of user devices associated with a user and a remote user device associated with a remote party, to a second device in the plurality of user devices associated with the user, the apparatus comprising at least one processor, and at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus at least to:

at the second user device, transmitting a request to a SIP registrar entity in the network to be notified of registration of user devices in the plurality with the network;

at the second user device, in response to the transmittal of the request to the SIP registrar entity, receiving a message from the SIP registrar entity indicating that the first user device has registered with the network, the message received from the SIP registrar entity comprising contact information for the first user device;

at the second user device, transmitting a request to the first user device to be notified of any communication sessions established with the first user device, wherein the request transmitted to the first user device is transmitted using the contact information for the first user device received from the SIP registrar entity;

at the second user device, receive, from the first user device, a message indicating that a communication session has been established between the first user device and the remote user device, the message comprising contact information for the remote user device, wherein the message indicating that a communication session has been established between the first user device and the remote user device is received in response to the transmittal of the request to the first user device;

at the second user device, in response to receipt of the message indicating that a communication session has been established between the first user device and the remote user device, configure a user interface on the second user device to display a call pull option;

at the second user device, receive user input via the call pull option displayed on the second user device; and

at the second user device, in response to the user input via the call pull option displayed on the second user device, transmit, to the remote user device using the contact information comprised in the message, a request to replace the communication session established between the first user device and the remote user device with a communication session between the second user device and the remote user device.

15. A computer program product comprising a non-transitory computer readable storage medium having computer readable instructions stored thereon, the computer readable instructions being executable by a computerized device to cause the computerized device to perform a method for moving an established communication session in a telecommunications network, the communication session being established between a first device in a plurality of user devices associated with a user and a remote user device associated with a remote party, to a second device in the plurality of user devices associated with the user, the method comprising:

at the second user device, transmitting a request to a SIP registrar entity in the network to be notified of registration of user devices in the plurality with the network;

at the second user device, in response to the transmittal of the request to the SIP registrar entity, receiving a message from the SIP registrar entity indicating that the first user device has registered with the network, the message received from the SIP registrar entity comprising contact information for the first user device;

at the second user device, transmitting a request to the first user device to be notified of any communication sessions established with the first user device, wherein the request transmitted to the first user device is transmitted using the contact information for the first user device received from the SIP registrar entity;

at the second user device, receiving, from the first user device, a message indicating that a communication session has been established between the first user device and the remote user device, the message comprising contact information for the remote user device, wherein the message indicating that a communication session has been established between the first user device and the remote user device is received in response to the transmittal of the request to the first user device;

at the second user device, in response to receipt of the message indicating that a communication session has been established between the first user device and the remote user device, configuring a user interface on the second user device to display a call pull option;

at the second user device, receiving user input via the call pull option displayed on the second user device; and

at the second user device, in response to the user input via the call pull option displayed on the second user device, transmitting, to the remote user device using the contact information comprised in the message, a request to replace the communication session established between the first user device and the remote user device with a communication session between the second user device and the remote user device.