Call Forwarding Assistant lets you route all calls made to your iPhone number to a different number.It allows you to setup call forwarding with one click.You can setup call forwarding destination from your contacts.
View in App Store
1)When you're home.You can forward it to your home number so you can use any extension in the house, and so you don't miss any calls while the iPhone is turned off or charging.
2)When you send your iPhone to Apple for battery replacement, you can forward the calls to your home or work phone number.
3)When you're traveling, you can forward the number to one of the Web-based services that answers your voicemail and sends it to you as an email attachment
4)When you're going to be in a place with little or no cell coverage , you can forward the calls to your hotel or a friend's cellphone. (Forwarded calls eat up your allotment of minutes, though.)