Here is a writeup of an approach for a Release 1 implementation that I quickly covered at the [onap-discuss] ONAP VoLTE SDC call held at 10:00pm China Time/10:00am Eastern US Time on August 2nd.
An alternate proposal discussed within the Modeling committee 3rd-Aug-2017, To bring consensus within the projects of ONAP involved within VoLTE usecase realization.