FXS Default is 'common area phone' so they can be used for analog phones. This can be modified to FAX or 'user mode' which adds voice mail box, and features using FAC (feature access codes) for a set of standard features.
The FXO are intended to be used for Telco line connections from a central office. Analog phones are not supported on them.
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...