The call is routed back to the routing client i.e. CVP or CUCM (wherever call arrived from) and follows dial-plan configured on the routing client i.e. CUCM Route pattern in matching partition or if CVP is involved either CUSP/CUPS/CVP dial-plan. If you are doing REFER transfer with CVP then the call gets routed back to the originating device i.e. ingress GW and a dial-peer is matched.