A variety of technologies to access the Internet is a reality today. An important subset of these technologies, which follows in full development, is the wireless networks. Given the technological alternatives and increasing demand for multimedia applications, preferably with connections AAA (Anyone Anywhere Anytime), interoperation between different wireless access networks is quite interesting. Following this trend, the IEEE (Institute of Electrical and Electronics Engineers) held a protocol specification that helps the process of handover between networks of different technologies (vertical handover) called IEEE 802.21 also known as MIH (Media Independent Handover). This work presents a study on aspects of mobility management and vertical handover process between UMTS (Universal Mobile Telecommunication System), WiMax (IEEE 802.16) and WiFi (802.11) technologies using IEEE 802.21 protocol. In it, there is a theoretical proposal of a decision algorithm for vertical handover between local and geographically distributed wireless networks to a topology commonly found today. Simulations involving vertical handover in these technologies, with the support of the IEEE 802.21 protocol, are performed using the software ns2 (Network Simulator). At the end, analyzes and conclusions of results are made.