Currently there are a wide range of applications for mobile devices. However, mobile devices with an inbuilt wireless interface card are known to have very small operating life. Energy plays a vital role especially for the usage of portable devices such as Cell phones, laptops and PDA's. In the scenario of unavailability of charging outlets it is often seen that these portable devices gets automatically turned off when the battery is consumed completely. This situation often arises when portable devices are used for applications like Voice over IP (VoIP) where a voice call is made through the continuous communication of packets over a period of time. Thus, it is essential to minimize the battery consumption during VoIP calls as opposed to just during periods where the device is not communicating. The well researched Green-Call algorithm provides a suitable solution by introducing a sleep time during the waiting period for arriving packets at the Client side. The amount of energy savings during VoIP calls with Green-Call depends on geographical locations of calling stations, network connectivity and data-rate. This thesis looks specifically at the impact of geographic locations on possible energy savings. Network characteristics encountered between calls made from the U.S to various continents are studied, and possible energy savings by the Green-Call algorithm are theoretically quantified.