I had an iPhone 3GS on AT&T for the last couple years....it was a good phone, but toward the end, it had trouble receiving calls. People said it would ring five times, but my phone did nothing. Didn't even recognize that I had a missed call. I upgraded to a Samsung Galaxy S3 (awesome phone, btw), and the same thing is happening. They told me to remove and re-insert my sim card, but I'm not optimistic this will help.
This is inexcusable, IMO. A phone should receive calls 100% of the calls that are made to it (especially when you have full cell service, like I do). Has anybody else had a problem like this?