Also known as: CW Call waiting is a phone feature that allows the user to be alerted, while they are engaged in an active call, that another incoming caller is trying to contact them.
Depending on the type of mobile phone, the user might be given an audible 'beeping' warning, or a message on their phone's display screen. This facility gives the user the option of finishing the first call before answering the second one, or alternatively the user could take advantage of call holding to keep the first call 'on hold' while the second caller is dealt with. Other options might be to reject the waiting call, or to send it to the voice mail service.