Here is simple configuration for VOIP traffic makes more efficiently handling by WAN or Interconnect.
Router-RTP-1(config)# class-map VOIP
Router-RTP-1(config-cmap)# match protocol rtp
Router-RTP-1(config)# policy-map VOIP_SHAPE
Router-RTP-1(config-pmap)# class VOIP
Router-RTP-1(config-pmap-c)# priority percent 75
Router-RTP-1(config-pmap-c)# compression header ip rtp