QoS over WAN connection for Voice Traffic

Well you can't!   Once its on the internet there are no guarantees of squat.  The only thing you have the ability to do is configure the router to classify the voice traffic and prioritize it when you send it out on the ISP link.    So you can control how you handle your outbound traffic, putting voice into the priority queue, signaling in a different queue and then the rest of your internet traffic in a default queue.    Unless the ISP is the voice provider as well as ISP, you won't have any guarantees once it leaves your router.  Now some ISP that offer voice service can give some guarantees, but if they are separate no guarantees.  How you do this depends.

If this is an MPLS connection, some ISPs have have a QoS chart specifying the various QoS options they support.  It is usually a service you pay for, and then they tell you in order for them to honor the service you would need to classify the traffic accordingly.  They want high prioirity traffic marked with a specific DSCP value, and when they see that they will put it in the appropriate queues on their network and honor that through their network.  If its not MPLS, then its a matter of just classify and schedule on the router in order to get your voice out first.  

Can you give more specifics to this setup?

Thanks