A Wi-Fi cell phone (also called a cellular-Internet phone or cell-Internet phone ) is a cellular telephone that can automatically switch between conventional cellular and Wi-Fi VoIP modes, even during the course of a conversation. A Wi-Fi LAN acts, in effect, as a cellular repeater for such a phone.
Wi-Fi cell phones are designed to prevent a phenomenon called drop-out that occurs when a cell phone set cannot maintain reliable contact with a repeater. Drop-out is a problem in dense urban areas and in concrete-and-steel buildings, which can block the radio-frequency (RF) signals between cell phone sets and outdoor repeaters. If a cell phone set is near the limit of a given repeater's range and the user walks from outdoors to indoors, loss of contact (a dropped call) can result.
With a Wi-Fi cell phone set, if the building has Wi-Fi access, the call is handed off from the conventional cellular network to the Wi-Fi LAN, taking advantage of VoIP technology to maintain the call without drop-out. Conversely, a Wi-Fi VoIP-based conversation taking place indoors, or within a Wi-Fi hotspot, can seamlessly transfer to the conventional cellular network if the user wanders out of range of the hotspot during the call.