12-10-2012 06:57 AM
Welcome to BlackBerry Support Forums
Have you tried your SIM on another Device or you can try another SIM on your Curve 8520 it will let you know if it a Network problem or the problem is within your device .Please go through this Knowledge Base :
KB03448 : Network status indicator shows " SOS " on the BlackBerry smartphone
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If Problem Resolves mark the post(s) as " Solution ", so that other can make use of it.