Incoming IP calls request a licence on reception of an incoming call. If no suitable licence is available the call is rejected silently (the application is not notified).
Outgoing calls request a licence after call_openout() is called. If no suitable licence is available then the call will not move into the EV_WAIT_FOR_OUTGOING state, but revert to EV_IDLE. Both incoming and outgoing calls subsequently release their licence when they are disconnected.