Sorry but what you're describing in NOT spot metering!
Spot metering is the ability to adjust exposure at a specific point in the frame. It has nothing to do with focus at all. Samsung tech support have confirmed that the S3 does indeed do exactly this, mine used to do it, approx 50% of the phones I tested to do it!
You choose a point where you the exposure adjusted to and that's what's supposed to happen. Any point, anywhere in the frame.
It's the same on any DSLR or any reasonably sophisticated point & shoot.