Nowadays phase locked loop systems are widely used in different devices that require signal synchronization, such as computers, GPS and others. Stability of such systems is an important problem for engineers. Linear stability for PLL can be studied using the well-known Nyquist stability criterion, Routh-Hurwitz criterion and others. However, it is also important for engineers to study so-called pull-in range, which corresponds to input frequency range which guarantees global stability of the system. In this paper frequency domain stability criterion proposed by G. A. Leonov is applied to estimate analytically pull-in range for the third-order phase locked loops. Analytical estimates are verified numerically.