Nothing in this chapter shall be construed to prevent any common carrier from furnishing free transportation to its officers, attorneys, agents and employees, and their families, and like free transportation to the officers, attorneys, agents and employees of other common carriers and their families, mail clerks, expressmen and sleeping car conductors and porters, and like free transportation according to its own regulations to persons devoting their entire time to religious work, and reduced rates to all other persons engaged in religious, charitable and literary pursuits, and for excursions, and for children and students attending schools and colleges, and for commutation tickets; or to prevent telephone, telegraph, sleeping car and express companies from entering into contracts with one another, and with common carriers for the exchange of services, or from exchanging with one another and with common carriers, the privileges of passes or franks for the officers, agents, employees and their families of such companies and common carriers.