I just bought an iPhone 3G on Sunday and I bought it with a leather protectice case. I've been using it all day plugged into my work computer with a USB listening to music and browsing my apps and I notice it is a little hot. Is heat dissipation an issue on these phones with cases on? Or is it normal for it to heat up slightly when using all day? It's not burning hot, but It's just a question I had.