Here are the steps to forward an AT&T phone line to another number.
1. Lift the receiver and listen for the dialtone.
2. Dial *72 or 72# and wait to hear the dialtone again.
3. Dial the number where you would like to have your calls forwarded.
TIP: If it is not a local number, you must dial the complete phone number; including the country code (e.g. +1), area code (e.g. 662), and telephone number (e.g. 323-0000). For example, 1-662-323-0000. You must also use this format for toll-free numbers.
4. Wait for the call to be answered. If you are forwarding to a fax line, wait for a fax tone.
TIP: If the call is not answered, the call forwarding process will not complete. If the call is not answered or if you receive a busy tone, you must repeat the process until your call is answered in order to begin forwarding your calls to that phone number.
5. Hang up the receiver after the call has been answered.
To turn off call forwarding, dial *73 or 73#.
Source: AT&T Support Portal http://www.att.com/esupport/article.jsp?sid=KB408811&cv=807#fbid=d6FZPIgArEI
