O/T/CSI (CAMEL) flag is a pointer to a specific CAMEL (IN) Service.
One of the CAMEL Service is Prepaid and this will align with a particular category value that indicates PrePaid / IN.
In the past I used to use HLR S-Types (Subscriber Types) to help with defining Prepaid customers. I used to use the S-Type value to help with splitting CDR / EDRs for Billing.
VBR/ Wallis Dudhnath