Look at the following book from Wiley:
CAMEL: Intelligent Networks for the GSM, GPRS and UMTS Network.
It provides a very good overview of CAMEL – from Phase1 to Phase4.
CAMEL Phase4.0 was standardised so that it can work with IMS. Last major standardisation work that was done with CAMEL was during the early 2000s.
VBR/ Wallis Dudhnath