Hi Michael,
CAMEL Phase 3 / 4 were standardised a long time ago. It was done well before the era of Gy, Gx, Sy, Diameter (RFC 7633), etc..
CAMEL Phase 2 is mainly used for Voice based Services – Call Control and Prepaid.
CAMEL Phase 3 supports MO-SMS and GPRS based Charging.
VBR/ Wallis Dudhnath