HELP, i want to add a prefix to the call number, any ideas ?

Hello

I want to add a prefix to the call number.
When i dial a number likee 1234 then my application should catch the dialing number 1234 and then change the the dial number as 9991234 and send the call to the 9991234 as a outgoing call.

i need :
1 - how to catch the call before it is executed ?
2 - how to build a program which runs in the background like that ?
3 - how to make the program starts with the phone system automatically ?

i am using
symbian S60 SDK 3rd Edition , FP2
Carbide.c++

Thanx