A computer platform with a Call Billing application thereon monitors linksets of the CCS/SS7 network extending between Local Exchange Carrier (LEC) Signaling Transfer Points (STP) and Competitive Access Provider (CAP) switches such as End Offices (EO) and Tandem Offices, where the CAP switches have access to the LEC switching offices in the LEC area for providing service therein. The platform receives SS7 Signal Units (SU) copied from the linksets and filters the SUs to pass ISUP MSUs of message types Initial Address Message (IAM), Exit Message (EXM), Address Complete Message (ACM), Answer Message (ANM), Reset Circuit Message (RSC) and Release Message (REL). The application correlates a received IAM against subsequently received and filtered ISUP messages in accordance with correlation search keys Originating Point Code (OPC), Destination Point Code (DPC) and Circuit Identification Code (CIC) so as to correlate the filtered ISUP MSUs that originate, set up and terminate a call. The elapsed time of the call is determined based on the difference between a call start time and a call end time where the start time is predicated on a call originating or setup MSU and the end time is predicated on a call terminating MSU. The call type can be for either "access" or "conversation" elapsed time depending on call direction and destination. Different ISUP MSU criteria are utilized for the two call types. For call type access, ACM may be utilized on which to base the start time, whereas for call time conversation, ANM may be utilized as the basis for the start time.