Single number reach setup is different depending on the phone service you have. If you're not sure, there's an easy way to tell.
Go to and turn on Single Number Reach.
After you've turned on single number reach and don't have call forwarding turned on, you'll see now instead of and when you hover over the icon, you'll see Single Number Reach is enabled.
Go to and select Open Call Preferences.
Go to the Single Number Reach tab and select + Add number.
Add a number and description and select Save.