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40 is about an average temperature but that depends on a few things - Your ambient temp and what you are doing and are you using 3G etc etc
It's normal that the phone gets hot while it's in use or when you charge it. If the phone gets too hot, it will automatically shutdown to prevent overheating.
This is normal because the video camera function consumes more power and memory. In such cases, you must wait a while until the camera is ready again to shoot video.