You can enable your call forwarding on the Verizon Website:
1. Go to the Call Forwarding page in My Verizon by clicking here.
2. Enter your deposit number in the Forward Mobile Number field.
3. Select the following option in the Options section: Forward calls when my line is busy.
4. Click Set Up Call Forwarding.
Note: If there's more than one line on your account, select the line you want to set up Call Forwarding on from the Mobile Number dropdown.
*Only available in the U.S.