If you want to be able to just plug it into yet another set of hardware at home... just go buy the stuff and plug it in.
Bluetooth is still a better deal than wired keyboard/mouse - but you still have the battery drain issue, which is why this is not a practical idea - especially since we're talking about an S3. It should be able to accept hardware input through the micro usb, but it's not really designed for that - and you'd have to get adapters and hub and why have all that crap taking up space if you already have a home system ? I wonder what would happen if you had three pieces of hardware trying to use the same micro-usb input, too (obviously, hubs work, but they have to share - and the monitor is going to want a lot of the available transfer capacity for itself) - makes more sense to just use it for HDMI to the monitor and use bluetooth for the peripherals.
If you had a phone that could run off AC only, it might fare better - since there'd be no battery constantly charging and draining and heating everything up, but the S3 won't do that.
Cool idea in theory ? Yeah. It would be great. But in practice, not so much. It would be better if the S3 could run from AC only - heck, it'd be almost a good idea. But since it can't and it lacks great cooling (since it's a compact, air-cooled phone), you're just going to be exposing the phone to high operating temperatures for extended periods of time which isn't exactly great for it.
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