Master Reset
To gain extra memory on your T300 select master reset and count 12.5 sec.
then release the battery to power off must be right @ 12.5 or retry till u
get it. By doing this you will wipe out all of the preset themes that
occupy so much memory! Warning pay attention 2 the master reset warning it
will also clear some temporary things stored on your phone.
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Sony Ericsson Tips