How to stop withheld numbers contacting your phone?

i have a prank calls sometimes and if i just ignore them they just keep calling and calling.. does anyone now how to stop withheld or unknown numbers reaching your phone? And my phone is sony ericsson so if anyone anything to stop them id love your advice! Also i don't want to keep changing my number! Thank you if you can help!How to stop withheld numbers contacting your phone?It's called unidentified caller or anonymous call rejection. Check services in the information pages in the front of your telephone book. You may or may not be charged for the service depending on where you live.