Any Problem in Letting iPhone 4 Battery Drop to 0? Is there any problem if I let my iphone 4 battery drops to 0%? I remember for older smartphones, once your battery flattens out all your data is lost, because they are stored in memory.

While I understand that iphone shouldn't have this problem, but I wonder whether is there any problem if the battery goes flat?
Not really. You won't suffer any data loss because the iPhone keeps everything on non-volatile flash memory. A complete discharge isn't great for the battery, but as long as it's not a regular habit your phone will be OK.