This paper presents a method to estimate parameters of a 3-phase line segment using PMU data. The novelty of this method is that it is capable of giving accurate estimates even in the presence of non-calibrated instrument transformers at both ends of the line whose ratio and phase correction coefficients are unknown. To do so, this method adds extra parameters in the regression model. These added parameters account for the errors present in the non-calibrated instrument transformers. In case the instrument transformers are calibrated at one end of the line, then the correction coefficients at the other end could also be estimated. The presented method does not require reversal of current flow direction in the line as a necessary condition. Results from simulated and laboratory experiments are presented to show the efficacy of the method. A discussion about analyzing the obtained results is also presented.