A system for locating a dual-mode telecommunication calling instrument communicating in or among a plurality of networks using two communication protocols, each respective network of the plurality of networks including at least one respective communication access unit coupled with a respective controller unit and a respective switching unit for routing communication to a called unit, includes: a data base coupled with each respective controller unit and with each respective switching unit. The data base cooperates with each respective controller unit to store location information substantially when the calling instrument begins communicating in the respective network coupled with the respective controller unit. The respective switching unit in the respective network coupled with the respective controller unit employs the location information to effect the locating.