You can set iPhone to forward incoming calls to another number. For example, you may be on vacation and want all calls to go somewhere else. If you're going to an area with no cellular coverage, you may want to forward calls to a place where you can be reached.

Set iPhone to forward your calls:
Choose Phone > Call Forwarding and turn Call Forwarding on.
Tap Forwarding To and enter the phone number you want calls forwarded to.

When Call Forwarding is on, an icon  appears in the status bar the top of the screen. You must be in range of the cellular network when you set iPhone to forward calls, or calls won’t be forwarded.