Congratulations! Your first day on the new job starts today. It’s a busy one, introducing yourself to a long list of existing clients. You pick up your cellphone and get to work. Hardly anyone questions the practice of conducting business on a personal cellphone, a ubiquitous telecom development that in 2010 became known as Bring Your Own Device.—or BOYD. Consider that according to research by Samsung, 61% of companies expect remote availability from employees—even those who are not provided a company phone. But the often-overlooked question here is, who pays for that business usage? The average cell phone bill...