Texas Government Code - GOV'T § 2170.010. Unlisted Telephone Numbers Prohibited

(1) to provide access to computers, telephone system control centers, long-distance networks, elevator control systems, and other tone-controlled devices for which restricted access to the telephone number is justified for security or other purposes;

(2) in narcotics undercover operations;

(3) in the detection of illegal sales of securities; or

(4) in the investigation of motor fuels tax fraud.