When Galaxy S3 was released on the market it was a true success, judging by the huge number of sales (20 million and rising). The device came with Ice Cream Sandwich installed though, and know all those 20 million users want to advance to the next level, the Jelly Bean 4.1.
A few days ago we found that UK has started rolling Android 4.1
to unlocked devices and now we found that Vodafone is going to release Android 4.1 to their users in the UK. The Over-The-Air update is available and rolling but it will not be released to all users at on time probably. Just stay close to your phone and you should be noticed when the update comes to you.
If you are not the waiting type, you can do a PC update using Samsung Kies. Remember you have to be subscribed to Vodafone or Three carriers in the UK.
UK is one of the happy cases that get Jelly Bean for Samsung Galaxy S3 before Christmas, as the US users are still awaiting for a specific date. Nothing is sure, but it is very probable that the US will get the update somewhere next year or at the end of this year.
If you can't understand why it is taking so long to bring the Android 4.1 to all Galaxy S3 devices, just imagine, 20 million devices that await this. It is impossible to release it in an instance to all devices and all those carriers on the market. In order for a carrier to release an update, it must first test its compatibility with the device, that's why unlocked devices get the update first.