You are running into a limitation of the technology you are using. Analog phone lines can only have a single number associated with a given line. You're best bet would be to direct calls to an auto attendant or a receptionist for call routing. If you require this functionality you will either need an ISDN line or a SIP trunk.
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...