Today, most portable devices, e.g., cell phones, PDAs, and laptops are Wi-Fi capable. Users can make efficient use of these devices by running various applications, including Voice over Internet Protocol (VoIP) to make calls. Portable devices are limited in terms of battery life, and hence the energy involved in the VoIP application is of concern. This thesis, presents experimental studies on the energy consumption of the devices using IEEE 802.11 Wireless LAN for making VoIP calls. The effect of high (G.711), medium (G.729), and low (G.723) bandwidth codecs on battery life was studied. This investigation shows that the G.723 codec is the most energy efficient. There exists an energy-quality tradeoff when selecting codecs. In this thesis, an adaptive algorithm, Efficient Codec Switching Algorithm (ECSA), is proposed. The ECSA utilizes a combination of codecs to minimize energy consumption of a VoIP call while meeting user-specified quality constraints. When using a laptop, these results demonstrate a percentage improvement of 6.43% to 24.1% over currently used codec schemes.