A 10-Digit Key Code to Your Private Life: Your Cellphone Number - The New York Times

Consider options such as Sideline (mentioned later in the NYT article) and Google Voice for a second phone number

"Yet the cellphone number is not a legally regulated piece of information like a Social Security number, which companies are required to keep private. And we are told to hide and protect our Social Security numbers while most of us don’t hesitate when asked to write a cellphone number on a form or share it with someone we barely know. 

That is a growing issue for young people, since two sets of digits may well be with them for life: their Social Security number and their cellphone number.

Nearly half of all American households have given up their landlines and have only wireless phone service — a figure that has risen more than 10 percentage points in just three years. Among people ages 25 to 29, the share of homes that have only wireless phone service stands at 73 percent, according to government statistics."

A 10-Digit Key Code to Your Private Life: Your Cellphone Number - The New York Times