Data handling system

In order to store data in a mobile telecommunications system, a data storage unit (HLR) has data functions (72,74) providing data redundancy therebetween, control functions (79,80) and signalling point (30,31,32) to enable the data storage unit to pass data to and from a mobile telecommunications network under the control of the control function. The control functions are physically separate from the data functions. The data functions (72,74) may operate on the basis that one has a primary data function, a second has a primary standby function to achieve synchronised updating. The use of separate and hence distributed functions enables greater flexibility in the retrieval of data from the data storage unit (HLR)