Heads Up :
The post you are writing will appear in a public forum. Please ensure all content is appropriate for public consumption. Review the employee guidelines for the community here.
Note that this pertains only to allowing applications to provide FAC or CMC for calls they may be attempting - there is no facility for an app to learn of any FAC or CMC used during a call they may be receiving.
Applications can determine the FAC or CMC used for a particular call historically via the Call Detail Record system: