The present invention provides a mobile unit (e.g., phone) for wireless communication that includes an antenna for detecting wireless fidelity (Wi-Fi) signals from a local area network and logic for switching the unit's operation from conventional cellular transmissions to Wi-Fi transmissions (i.e. 802.11) upon detection of Wi-Fi signals. The handheld device can communicate with a Public Switched Telephone Network (PSTN) using Voice Over Internet Protocol VOIP. In one embodiment, the logic for performing the switch to Wi-Fi transmission is programmed into a subscriber identity module (SIM) card in the device and can perform the switch automatically or in response to manual input after prompting the user. Memory and code in the mobile unit measure and store the duration of both cellular and Wi-Fi transmissions by the mobile unit.