how many clients do you have? have you tried different channels and width?

we are not able to change the dns provided by comcast. The one you input under lan settings will be shown on your computers and phones once they are connected to this router.

there is a setup video, you can have a look first. http://www.tp-link.com/us/download/HS200_V1.html

have you switched it on and off three times? (you should press that switch 6 times and every time leave 2 seconds each time. Then you will see the light blanks three times. You can also try switched...

how do you want to use it? IOGear GWU637 provide internet to C8 or C8 provide internet to IOGear GWU637?

how about dmz for the voip phone? and disable SIP-ALG? if no changes, it is suggested to contact tp-link support.