Twinning allows a primary extension and a secondary number (extension or external) to operate together as a single telephone, typically used in scenarios like workshops or warehouses where team supervisors may have a desk with a fixed phone but also have a Mobile/Cell phone. When a call is presented to the primary phone the secondary will ring. If the primary telephone does not ring, for example in Do Not Disturb, the secondary phone will not ring. When a call is made from either twinned phone, the call will appear to have come from the primary phone (when the secondary is an extension on the IP Office system). Other users of the system need not know that the supervisor has two different phones. The supervisor’s Coverage Timer and No Answer Time are started for the call and if the call is not answered within that time, the call will be delivered to available coverage buttons (if applicable) and then Voicemail (if applicable). Users may be allowed to enter a twinned number, or may just be able to activate/deactivate the twinning function depending on administrative settings.