Something I was looking into as part of some recent work I was doing is the ability to have receptionists at multiple sites who can operate together as one team, effectively pooling their resources together so that call volume to a single site doesn't really matter. If there are too many calls coming into one site then receptionists at other sites will see this and can answer the calls as if they were local to that site.
This feature in the Cisco Unified Attendant Console is called remote attendant. And this it is further described in the design guide, see the below link.
Just one thing to be aware of though when considering the remote attendant feature is that there needs to be the ability to transcode across the WAN, I.E. you'll need an ISR at each site with receptionists and some DSP resources in the ISR.
References:
Unified Attendant Consoles Design Guides
http://www.cisco.com/en/US/products/ps7282/products_implementation_design_guides_list.html