When you enter a call-forwarding phone number you must use a specific format:
Your country code (1 for the United States)
Your area code
Your phone number (use only the phone number’s digits; do not use hyphens, periods, parentheses, etc.)
For example, if the phone is in the United States and the phone number is (425) 555-1234, you would enter the phone number like this:
To add or edit a number
In the Phone number box, type or edit the number, and then click OK.