Sony Ericsson Z550i, problems

@Warmedal (397)
April 16, 2008 2:30am CST
I have a Sony Ericsson Z550i and I have owned this phone for almost 2 years. Since the last 6 month, it behave really strange like random restarts and I often get "SIM-card inactive" when I receive sms. I have the latest software in it, I even returned it once to repair but they didnt found any problems, anyone know what the problem might be?
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