Methods and systems for determining whether a mobile radio terminal is on or out of a zone in a radio communications network. The methods and systems provide for generating a profile representative of the zone using measurements taken by the mobile radio terminal and/or the network and/or using predicted values. A comparison is then made between subsequent measurements or values and the profile to make a determination as to whether the mobile radio terminal is in or out of the zone. The methods and systems are applicable to any zone-based application including differential call charging, security applications, buddy finder services, mobile gaming and location based services in general.