Click-To-Call or CTC is a service which lets users click a button and immediately speak with a customer service representative or other user. The call can either be carried over VoIP, or the customer may request an immediate call back by entering their own phone number. One significant benefit to click-to-call providers is that it allows companies to monitor when online visitors change from the website to a phone sales channel.
CTC also describes a form of advertising that offers either desktop or mobile users the ability to click a phone number or button embedded within an advertisement in order speak to that business over the phone.