The function allows you choosing a number that you want in order to
light up during the call to traditional telephones. You can also unlist the
number and it won’t light up.
Telephone service companies have created a special communication service without the need to use customer's equipment. It's called a "virtual number". It also has a text type of "virtual SMS center." Thanks to the virtual link you can make calls or send messages while connected to the equipment of the company.