Call forwarding (or call diverting), in telephony, is a feature on some telephone networks that allows an incoming call to a called party, which would be otherwise unavailable, to be redirected to a mobile telephone or other telephone number where the desired called party is situated. In North America usually (though not always) the forwarded line rings once, to remind the customer using Call forwarding that the call is being redirected. More consistently, the forwarded line indicates its condition by stutter dial tone.
In Europe, most networks indicate that unconditional call forwarding is active with a special dial tone. When the phone is picked up it is immediately apparent that calls are being forwarded.
When and Why to Use it
Diverting calls can increase one's availability to a caller. The main alternative is an answering machine or voicemail, but some callers do not wish to leave a recorded message, suspecting that the party will delay returning their messages.
Some businesses find that the human touch can improve contact, thus sales, but traditional wired answering services are expensive, so they have their calls forwarded to a call center, so the client can reach an operator instead of an answering machine or voice mail.
Some services offer international call forwarding by allocating for the customer a local virtual phone number which is forwarded to any other international destination.