We've found 3 ways different people like for their Reception:
1/ DID form points to a ring group, back-up receptionists have a Group Presence button to make themselves available when required. When nobody is logged in, it can overflow to head office, or to voicemail. Users can use the correct feature access code to forward the ring group to another office or direct to VM if required.
2/ DID form points to a Multi line key - put the key on any of your users who wants to be able to pickup Reception
3/ DID form points to a number that is permanently re-routed to a mailbox with Call director on it, call director qualifies what the caller wants and transfers the call to whichever ring group is relevant, or to voicemail