Your BlackBerry rings -- it's a 1-800 number. Again. Or even worse -- it's your ex. The way to stop calls from coming to your BlackBerry is to use one of the many call blocker applications available. Most of these applications come with a blacklist. When you put a phone number on the blacklist, that number will no longer be able to reach you. You can also customise most call blocking programs to stop unknown or private callers.
Use Call Blocker Pro, an application that you can purchase at BlackBerry's App World. You can set up Call Blocker Pro to block calls from specific numbers or calls that come in at specific times -- for instance any call that comes in after you've gone to sleep. As of June 2011, the app costs £3.20.
Use Call Blocker Professional. You can set up Call Blocker Professional so that when someone calls you the call is transferred directly to voicemail or the call is simply disconnected so they can't leave you a voicemail. You can also block private numbers and unknown numbers. Call Blocker Professional costs £1.90 as of June 2011.
Use Call Annihilator. You can set up a blacklist that prevents any numbers you choose from contacting you. You can also block groups -- for instance, any 1-800 number. You will receive no notification when a call is blocked, but you can view the last 50 blocked calls. As of June 2011, Call Annihilator costs £3.20.
If you remove the application from your BlackBerry, all of the blocked numbers will be able to reach you again.