Welcome to Vodafone Community
Whether I make a phone call or whether I am texting or even not doing anything, the S3 just switches itself off for no reason.
Does anyone else have this problem ?
If it's a faulty 'phone, I want a new 'phone because it is really unprofessional.
If a Phone shows any sign of malfunction within the first 7 days, you should always return it...
Your only option now will be a Free Warranty repair.
Either with Vodafone or directly with Samsung.
I am aware of the 7 day or 14 day rule depending on the method of purchase.
The first time it happened, I thought I had switched it off by accident whilst making a call.
It don't think it did happen in the first seven days.
The title of your post states... "Samsung Galaxy S3 turning itself off randomly since day one"
So I assumed that was the case, my apologies if I misunderstood!
However your options remain the same, you can contact 191 or hang on for one of the Team to contact you. Or if you prefer you can go directly to Samsung.
A guy at work had this problem with his S1 a few months ago so brought it to me to inspect. I put it down to corrupt firmware and reflashed it with a new stock rom and this cured the problem. If you haven't updated to Jellybean yet then see if it will update and take it from there. If it still does it then you can either send it in to Vodafone or Samsung for repair or flash it with a clean stock rom. Soupdragon has a smashing step by step guide that even your granny could follow!
This is a Firmware Issue as said above the Vodafone S1 was plagued with this my own phone had a corrupted firmware
Now a factory reset will not fix this, if its outside the cool of i would avoid sending it back to Vodafone and take it to a samsung service centre and get them to sort this out
There is a way to do this yourself but as its so new i would let Samsung sort this