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Hi Mijing,
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Try downloading the settings for the device.
Menu > Settings > More > Internet Settings > Accept disclaimer > Choose network.
Once done see if 3G is back up and running.
Its possible that you may need to replace the SIM card, have you tried with other SIM cards yet?
Then the issue is your SIM card, unfortunately you are going to have to replace your SIM card. Although they work in other devices this does not mean that they are not the cause of the problem, and your testing confirms this.
No problem, I hope it all works out for you 