The universal line model (ULM) is a transmission line model developed directly in the phase domain that is recognized for its accuracy and generality. It is currently the reference model for transient studies, but is exclusively found on commercial electromagnetic transients programs. This paper describes an implementation of ULM in the Alternative Transients Program (ATP), which is free for licensed users, using the foreign models tool and the type-94 component available in this platform. The implemented model is validated through comparisons with EMTP-RV. Then, it is used to investigate transients on overhead transmission lines considering a rigorous representation of the ground return impedance and ground admittance assuming frequency-dependent ground parameters.