The redial button allows the last telephone number called to be called again with just a touch of a button. The associated function is called redial and is available on most telephones. The redial button is often represented by two intertwined rings. The redial button allows the number to be redialed significantly faster and not having to have the number right in front of you or remember it. The redial button is often used to call a busy number repeatedly until the line is free. Redialing is used for land lines as well as in Voice over IP (VoIP) and mobile phones. The redial button is typically also found on fax machines.
The standard redial button enables the basic redial function. This simple implementation only stores one number to redial. Every time a call is placed, the phone saves the last number dialed to this memory. Previous contents are overwritten. Pressing the redial button will call up this memory and automatically dial the number. This only allows the last number called to be redialed. It can be redialed until replaced by a different number called.
Modern phones, cell phones and smartphones with display typically feature advanced redial functions. This allows access to any number from a large redial memory. So you may access one of the last ten (or more) numbers dialed at the push of a button.
Even if a phone doesn’t have a redial button, it may possibly redial. After all, this function can not only be provided on the devices themselves, but also via switchboards or telephone systems. In this case a central server stores the last number dialed from a phone. A defined key sequence can then be used on a device to redial.