Resolution
To change the prefix dialing digit for access to an outside line in Cisco CallManager, go to Route Plan > Route Pattern and change the prefix number from "9" to x (where x is the desired prefix digit), as such:
Route Pattern* - 9.5816XXX
Note: In the event, "9" must be sent along with the number to complete the call, add "9" under Called Party Transformations for Prefix Digits (outgoing calls).
For detailed descriptions and examples, refer to the Wildcards and Special Characters in Route Patterns and Hunt Pilots section of Understanding Route Plans.