On WAN you setup LLQ to prioritize voice traffic and other classes to map to what the provider PE (carrier WAN side) router is configured for, but sounds like this is an Internet connection, so even though you can still prioritize traffic on the egress of the router to queue traffic accordingly, but it does very little as on the public internet none of the traffic is prioritized and the DSCP markings are ignored. Hence, with internet based SIP connection you cannot deliver QoS.
