a nomadic server and a related system provides seamless roaming for a mobile communication device between different types of wireless networks , such as wifi and cellular networks for voice , data and video communication . use of the nomadic server enables a combination of wifi and cellular networks for providing access to cellular phones and make use of the voip networks for switching the calls wherever possible . the nomadic server is a telephone communication processing and switching server that will “ hold ” the present , in - progress telephone communications without dropping , while roaming without losing the present , in - progress communication . for example , a telephone communication can be seamlessly switching between voip and cellular telephone networks using the nomadic server . nomadic server resources interface with the voip and cellular network switches to provide the hand - off between networks . this approach enables switching of telephone communications over a voip network wherever possible either through wifi or through cellular networks .