How do i block phone numbers from my mobile phone?

How do i block someones phone number from a Sony Ericsson w595 (The phone make and model might not count :P) Anyways, Is it possible to do this? and if so how do you do it?How do i block phone numbers from my mobile phone?
You would have to ask the mobile phone company to do this for you and it would depend on the company whether they charge for this or not. Easiest is to put the phone number of the person you want to block into your directory with an X and every time the X comes up as person calling, you can ignore it.