A simple manipulation allowing you to block unwanted calls and SMS on your Windows Phone 8 device:
Enable call blocking:
- Swipe the StartScreen from the left edge to the right and go to Settings.
To block a contact:
- Tap on "call+SMS filter".
- Open the call list of your Windows Phone 8 device.
- Press and hold the number you want to block for a couple of seconds.
- A small menu shall be displayed, select the "Block number" option.