Setting up Call Interception Codes is fairly easy. You just need to go Settings and type in your desired prefix/prefixes under Interception Codes. And Viola! Next time any call made to a number starting with such predefined prefix/prefixes will directly go through CoolDialer.
This options gives you the flexibility of choosing which calls you want to make using CoolDialer. If prefixes are predefined, you do not need to open the CoolDialer Application every time you try to make a call. These calls can be made from your typical phone calling interface.
For example, you have set '+' or '00' as your interception prefix on the CoolDialer. And the dialer is running in background, so if you make a call from the phone interface starting with '+' or '00', this call will go through Cool Dialer, other than directly through your operator. For ease of use, you can use international country codes (especially the ones which are frequently used) as prefixes. Basically any prefix can be set by the user and if you do not want any, all the prefixes can be removed from the Settings.