if there are more extensions than phones I assume you are just needing voicemail for each employee? If that is the case you create users with assigned extensions and voicemail boxes. Then set up a cheap spa301 in a common area. Now each employee without a phone can check voicemail at the 301 by dialing the vm pilot, press * then follow prompts to check vm. Or you could do voicemail to email.
Configure Multicast Paging on the Cisco IP Phone 7800 Series or 8800 Series Multiplatform Phone
The Cisco IP Phone 7800 and 8800 Series Multiplatform Phones provide voice communication over an Internet Protocol (IP) network...
Add Call Park on a Cisco 7800 or 8800 Series Multiplatform Phone Key Expansion Module
Call park allows the user of the phone to put an incoming call on hold so that the call can be retrieved on another phone. A call is park...