VoIP voice packet priority

Hi folks, I am interested in setting up a VoIp system - looks like our internal stuff is OK but we are concerned about getting priority for voice over data on Comcast side of modem. We can set up on our router equipmewnt but am concerned about running into call quality issues if i use a large amount of bandwidth. I know that most ISPs strip the tags off the voice packets once they cross over the circuit.  Can you prioritize voice traffic, or do you by default, on your end? 

here it is again - does Comcast prioritize voice traffic? Thanks