In this paper we present techniques for allowing Mobile IP to interwork with wide area cellular networks. As an example, we illustrate a network consisting of a GSM general packet radio service (GPRS) air interface and a Mobile IP backbone network. The advantage of such a solution is that the backbone network may easily be used to support integrated wireless and wired data transfer, and the leveraging of standard data networking protocols and equipment will reduce the cost of wireless data networks. We present issues and suggested solutions for mobility management functions, such as detecting changes in points of attachment to a network, micromobility, roaming, and paging, and security functions, such as authentication and ciphering. We show which elements of each network, GSM and Mobile IP, may be re-used, combined, or eliminated to provide a single, unified network.