However, in order to complete the forwarding process, you may be required to enter an Online Authorization Code that we'll send to your mobile device as a free text message. In most cases, you must have your mobile phone with you to receive that code and verify your identity.
If you're an Account Member on your account, you may be able to send the Online Authorization Code to the Account Owner's phone instead. For instructions, go to the Turn off Call Forwarding from your computer section of our How to Use Call Forwarding page.
*Not currently available for prepaid accounts. Call Forwarding can only be turned on by calling from your prepaid mobile phone.
From Call Forwarding FAQs