If UE in RRC idle mode (no data active) is VoLTE call possible?
If yes then how?
Yes, VoLTE call is possible.
UE will trigger a SERVICE REQUEST on last camped cell and complete VoLTE call.
But if you question is: can VoLTE call can go in RRC idle mode?
Then Answer is NO.
There are no drb/Srb in IDLE mode for any data to flow.
UE will be changed to rrc connected mode, to setup bearers with ims network.