I have an iPhone 3G, with AT&T. Yesterday, I was foolish, and installed a 3.0 beta on my device, with iTunes 8.2. I had to downgrade to iTunes 8.1, DFU my iPhone, re-sync my music, and I have to re-DL my apps. The one thing is, even though my SIM Card is inserted (And I tried taking it out + putting it back in), I still have zero signal bars, and the AT&T carrier logo doesn't appear. What do I do?