A communications system having a unified communication architecture that provides unified voice messaging services and data services via an internet protocol network and comprising: a network; a plurality of communications devices (108a-108n; 112a-112n), being associated with a user, operably coupled to the network, each communications device being operable to enter a low power state in response to a "hibernate" command; and a server operably coupled to the network, wherein the server comprises a power management unit configurable to provide the "hibernate" command to the one or more communications devices, wherein a) the power management unit generates a non-preferred device list based on a preferred device list, the non-preferred device list comprising the plurality of communications devices (108a-108n; 112a-112n) associated with the user that are not specified in the preferred device list, b) incoming calls are routed to at least one preferred communications device of the plurality of communications devices (108a-108n; 112a-112n) specified in the preferred device list by means of software using said preferred device list, c) the power management unit monitors presence information of the user and generates an unused device list based on a change in the presence information of the user, d) the unused device list comprises at least one unused communications device of the plurality of communications devices (108a-108n; 112a-112n) that are not to be used by the user due to the change in the presence information, e) the power management unit merges the non-preferred device list, and the unused device list and generates a "hibernate" device list, f) the power management unit sends a "hibernate" command to at least one communications device in the "hibernate" device list and g) the "hibernate" command causes the at least one communications device that receives the "hibernate" command to turn off all circuits except a power management module of that device to enter a low power state, and h) the server comprises a presence service unit which maintains presence information associated with at least one user. a network; a plurality of communications devices (108a-108n; 112a-112n), being associated with a user, operably coupled to the network, each communications device being operable to enter a low power state in response to a "hibernate" command; and a server operably coupled to the network, wherein the server comprises a power management unit configurable to provide the "hibernate" command to the one or more communications devices, wherein a) the power management unit generates a non-preferred device list based on a preferred device list, the non-preferred device list comprising the plurality of communications devices (108a-108n; 112a-112n) associated with the user that are not specified in the preferred device list, b) incoming calls are routed to at least one preferred communications device of the plurality of communications devices (108a-108n; 112a-112n) specified in the preferred device list by means of software using said preferred device list, c) the power management unit monitors presence information of the user and generates an unused device list based on a change in the presence information of the user, d) the unused device list comprises at least one unused communications device of the plurality of communications devices (108a-108n; 112a-112n) that are not to be used by the user due to the change in the presence information, e) the power management unit merges the non-preferred device list, and the unused device list and generates a "hibernate" device list, f) the power management unit sends a "hibernate" command to at least one communications device in the "hibernate" device list and g) the "hibernate" command causes the at least one communications device that receives the "hibernate" command to turn off all circuits except a power management module of that device to enter a low power state, and h) the server comprises a presence service unit which maintains presence information associated with at least one user. a) the power management unit generates a non-preferred device list based on a preferred device list, the non-preferred device list comprising the plurality of communications devices (108a-108n; 112a-112n) associated with the user that are not specified in the preferred device list, b) incoming calls are routed to at least one preferred communications device of the plurality of communications devices (108a-108n; 112a-112n) specified in the preferred device list by means of software using said preferred device list, c) the power management unit monitors presence information of the user and generates an unused device list based on a change in the presence information of the user, d) the unused device list comprises at least one unused communications device of the plurality of communications devices (108a-108n; 112a-112n) that are not to be used by the user due to the change in the presence information, e) the power management unit merges the non-preferred device list, and the unused device list and generates a "hibernate" device list, f) the power management unit sends a "hibernate" command to at least one communications device in the "hibernate" device list and g) the "hibernate" command causes the at least one communications device that receives the "hibernate" command to turn off all circuits except a power management module of that device to enter a low power state, and h) the server comprises a presence service unit which maintains presence information associated with at least one user.