Yes, in case of an emergency you must have a communications device such as a cellular phone or two-way radio when transporting a child.

Source Note: The provisions of this §747.5421 adopted to be effective September 1, 2003, 28 TexReg 1462; amended to be effective April 15, 2017, 42 TexReg 1906; transferred effective March 9, 2018, as published in the Texas Register February 16, 2018, 43 TexReg 909