While Asterisk does a good-enough job of generating and storing CDRs, the records are in a very raw format, which makes it difficult to perform any sort of analysis on them.

Enter the CDR reporting package. In the 1990s, when long-distance rates were complex and expensive, an entire subindustry was spawned by companies looking to help other companies make sense out of complex long-distance rates. Nowadays, with long-distance being far less expensive, as well as generally simpler in terms of pricing model, there is less need for detailed analysis of call records. Nevertheless, many of these highly experienced companies have added support for Asterisk CDR analysis, and thus if you want excellent reporting capabilities, you will find a huge industry with many experienced participants.

For a simple interface to the call records, a popular program is CDR-Stats, which is the successor to the hugely popular Asterisk-Stat package. This open source reporting interface provides a simple way to examine call detail records, and some basic metrics on calling patterns.