I recently had my iPhone 3GS 8GB replaced at the Apple store because of a faulty power button (and cracks near the headphone jack and dock connector). I noticed that if I slap (with my hand) my replacement iPhone 3GS, it says "No SIM Card Installed" and then it goes away and about 10 seconds later, it shows an AT&T 3G connection. This is odd. Is it a hardware issue? Is it relevant that my iPhone is jailbroken (greenpois0n rc6)?