In Microsoft Lync 2010 we provide support for E-9-1-1 to dial emergency services in United States. In order for the emergency services to be able to get in contact with the person making the emergency call, the Lync 2010 client automatically disable the Do Not Disturb (DND) state, if it is set, and disable any call forwarding rules active on the client prior to making the emergency call. The inbound routing component on the Lync server will also act on this flags and disable the user’s own call to voice mail.
You can observe the presence state change and call forwarding being set to off in the client as soon as you dial the emergency dial string. The client will re-enable the call forwarding rules after 2 hours. The way this is done is to publish a time-bound routing category with the e911active flag set (for more information see http://msdn.microsoft.com/en-us/library/ff530304(office.12).aspx and http://msdn.microsoft.com/en-us/library/ee682734(v=office.12).aspx).
You can reset the e911active flag by manually changing the call forwarding rules on the client.