Go to the top of the Contacts list in the Phone app. See how it says "My Number"? It's for that. You can put any number you want there (for ex., if you have Call Forwarding on you can have it show the number you're forwarding to).
Go to the top of the Contacts list in the Phone app. See how it says "My Number"? It's for that. You can put any number you want there (for ex., if you have Call Forwarding on you can have it show the number you're forwarding to).