assuming that the phone has not been water-damaged, it may need to be re-flashed, sony-ericssons do freeze quite often for no apparent reason, and re-flashing the phone often (but not always) fixes this prob. You will need to take it to a dealer, they will charge you for this. (There is normally a water-ingress indicator label on most phones, these are small circular sticky labels, that are normally white, however these turn Pink/Red if the phone has been subject to water-damage, if it has gone Pink/Red, then generally a dealer will not touch it, these lables are normally placed somwhere inside the battery compartment, somewhere visible so that a dealer can quickly check them).....
Paul_01
July 2010