How do you block a phone number on a cell phone?

How do you block someones phone number on a cell phone?

Call the company anf tell them, they don't have to know why, but if they ask, make something good up. Just let them know you do not want this person(s) calling anymore and would for them to be blocked from calling ASAP.

U have an option in phone to blacklist someone...U can make an accepted list and accept from them only..If you are using a phone with symbian oS you can try the app Blacklister

where on the phone is the option to block a number?