Power Shock / Leakage on iPhone 3Gs

Hi,
I discovered that there is some form of power leakage from my 3Gs today which results in a minor electric shock.
I have a unibody (Alu) Macbook. I had the iPhone charging through a usb wall adaptor because of low charge. Whilst typing I picked up the phone to make a call (iPhone still charging). I discovered that if my hand was resting on the MBP's case when I put the phone to my ear, I received a mild shock through my ear when my ear touched the metal bezel (surrounding the screen) of the iPhone. The MBP was also connected to mains power on another socket by the way. I also discovered that as I moved my fingers over the MBP case with the phone at my ear, that I can feel a current passing through my fingers to the MBP case (felt as a mild tingling vibration). As soon as the phone is held away from the body the vibrations and shocks disappear.
Has anybody else experienced this ? Has anybody any idea what the effect on the MBP is of passing current through it's shell ? (must be small, but I dont want to fry any chips ....)

Thanks

Paul