With the proliferation of a multitude of diverse yet coexistent array of networks in the recent past, the heterogeneous environment is foreseen to serve mobile terminals (MT) in a complementary fashion at large. Multimodal MTs can now switch interfaces between Wireless Local Area Networks (WLAN) and the cellular network. In order to exploit the heterogeneity of the wireless environment, MTs require smart medium selection methods. In this paper, we derive a practical yet tractable method of evaluating vertical handover (VH) algorithms for mobile voice users over heterogeneous environments. The random direction and the Gauss-Markov mobility models are analyzed as an extension to the previously studied random waypoint model. The performance of a VH algorithm is evaluated for an MT roaming in and out of the WLAN coverage area under these mobility models. The analytical procedure is utilized in deriving the required signal strength thresholds upon which an MT bases its handover decisions for a given outage probability.