Kindly read the description carefully and don't forget to  examine the mentioned application before you reply.

To implement this application developer must need  experience in iphone development Ruby script/MAC OS X/perl programming since these are the part of the application requirement to give application below mentioned functionality by keeping in mind that required functionality doesn’t comes with apple official API.

Apple API doesn’t allows multitasking and doesn’t allows you to read the caller ID buffer as a call arrives neither to read the incoming call history log file, the developer will have to come up with a solution for that.

I know this is something can be done since there are applications outside (see below) have the above mentioned capabilities (multitasking + reading the incoming caller ID buffer as a call arrives). Below is a list of application implemented exactly the functionality I’m looking for my application as they know how to read the incoming caller ID buffer as a call arrives and do an operation in conjunction to the OS, means multitasking. 

McallShow – this application is sort of Caller ID which have the exact capabilities we need for our application to fully function. This application read the caller ID buffer as a call arrives and then send a query to the database.
http://iphonefreakz.com/2008/11/19/cydia-mcallshow-12/

iBlacklist – this application must access the incoming call/text history log file and also to have multitasking and to be able to read the incoming caller ID buffer in order to function.
http://www.iblacklist.com.br/iblacklist/index.php
To read full details about the way it works:
http://www.appleiphoneschool.com/2008/06/16/iblacklist-191-filter-incoming-calls -and-texts/


Mcleaner – same application as the above mentioned.
http://iphonefreakz.com/2008/06/03/mcleaner-14rc1/

Backgrounder - Lets you multitask on the iphone.
http://code.google.com/p/iphone-backgrounder/wiki/Documentation