CDRs for billing are delivered by FTP 'push' from the UCM. UCM can be configured with up to three destinations for CDR records (flat, comma-separated format files), where they will be delivered periodically via FTP.
There is a SOAP interface - CDRonDemand - for retrieving single CDR files, however this interface is not intended for billing data delivery.
CDR documentation: see 'Cisco Unified Communication Manager Call Detail Record Analysis and Reporting Administration Guide'
CDRonDemand documentation: see 'Cisco Unified Communications Manager XML Developer Guide'
Both available here:
http://developer.cisco.com/web/sxml/docs