All the credits go to iClarified @ http://www.iclarified.com/entry/index.php?enid=953
These are instructions on how to filter your incoming calls and SMS messages using iBlackList for iPhone.
iBlackList allows your to create a blacklist or whitelist for filtering purposes. iBlacklist also features a scheduler which allows you to set the time of day iBlackList is active. The unregistered version of iBlackList allows you to filter 2 numbers. For unlimited numbers your must register. Please see the link at the end of this tutorial.
Step OnePlease make sure you have iClarified added to your list of installer sources. To do this click
here.
Step TwoPress to launch
Installer from your SpringBoard.
Step ThreePress to select the
Install tab at the bottom of the screen.
Step FourPress to select
iClarified from the list of Categories
Step FivePress to select
iBlackList from the list of Packages
Step SixPress the
Install button at the top right of the screen.
Step SevenPress the large red
Install button that appears.
Step EightYou will be notified that you must restart iBlackList once install has been completed. Press the large
OK button.
Step NineYou will be returned to the Categories menu when installation is complete. Press and hold the
Sleep/Wake button for 3 seconds until the Power slider appears. Move the slider to the right to power off your iPhone. Then press the
Sleep/Wake button again to turn your iPhone back on.
Step TenFrom the SpringBoard press to launch your new
iBlackList icon.
Step ElevenYou will be asked to enter a password. Input the number 1 and press the
Confirm Access button.
Step TwelveYou will now be taken to the iBlackList home screen. Lets first move the
Enabled switch to
ON to enable iBlackList.
Step ThirteenNow to add a number to our BlackList press the
BlackList button.
Step FourteenPress the
Add button at the top right to Add a number.
Step FifteenHere we can enter a contacts information in manually or press the
Contacts button at the top right to input information from your phonebook.
Step SixteenSelect a contact from your phone book and then select the phone number you would like to blacklist.

The Display and Phone number fields will then be populated automatically. Press the
Add to list button.
Step SeventeenNotice the number is now added to your BlackList. Press the
Back button at the top left to return to the iBlackList menu.
Step EighteenScroll down and ensure
Active Mode is set to BlackList. Note: if you want to setup a whitelist of course you would set active mode to WhiteList.
Step NineteenPress
Settings Calls to modify the settings for call filtering. Here you can set the action to take when a filter call comes in. You can also enable or disable the call filter and set the preferences to save history, delete recent calls, filter restrict number, filter unknown number, show a status bar icon, and vibrate. Press the
Save button at the top left hand corner when finished modifying the settings.
Step TwentyWe can also press
Settings SMS to modify the filter options for SMS messages. Here you can enable or disable SMS filtering and set the preferences to save history, delete SMS upon receipt, filter unknown number, show a status bar icon, and vibrate. Press the
Save button at the top left hand corner when finished modifying the settings.
Step Twenty OneYou can press
Scheduler from the main menu to set the iBlackList's operation schedule.

Press to select a day of the week and you can modify the hours iBlackList is enabled for that day.

Press the
Save button at the top left to return to back to the iBlackList menu.
Step Twenty TwoFinally you can also change your password by pressing the
Password button on the main menu. Enter a new password and then press the large red
Save password button.
Step Twenty ThreeYou can now press the
Home button to exit iBlackList. When ever you receive a filtered text or call you will notice an icon in your Status bar. Press to launch
iBlackList from the SpringBoard.
Step Twenty FourPress
View History from the iBlackList menu.
Step Twenty FiveYou will now be able to view your filtered call or message and respond accordingly!


THANKS***:
Thanks goes to the iDevBrTeam (Daniel Antonio, Alexandre Kremer). You can visit their site to register iBlackList for a small fee.
http://www.iBlackList.com.br