I have tried it all. After that I went to the customer care center where the customer care guy tried my SIM card in another blackberry device, and it worked well. But when I put my SIM in my own device it stopped working.
He told me that there is some problem with my device and no problem whatsoever from their side. As the handset is from T-Mobile he refused to fix the hardware/device issue.
Is there any other option that I can try.