If you are using Windows Phone 8.1 and above then you should have the option to edit the DNS servers used by the phone. We have put should in italics as this feature is still broken on lots and lots of Windows phones. Never the less here goes:
- Go to settings
- Choose Wifi
- Press and hold the Wifi you are connected to
- Select Edit from the pop up
- If the fields are greyed out then you have the bug as many other Windows Phone users and you won't be able to edit the DNS. Instead setup your router.
- If you can enter values in the fields then set DNS to 18.104.22.168 and press done.
- You might need to restart the phone.