I'm considering buying boxed CD key for Battlefield 3 Premium, as it has significantly better price than one in Origin Store. Are these keys region restricted in any way?
I can tell you from personal experience, I bought a Bf3 CD key from one of the bigger cd key websites that was not a Russian key but a normal English key.
It worked for for about two weeks then my Bf3 got its key disabled and I couldn't start it anymore. I got a refund from the key supplier and purchased a copy from amazon and put in the new key. It accepted the key but it wouldn't run either. When I contacted EA, they said the account was disabled.
I had to argue with the online support for a few hours to get my amazon key working. Finally after being persistent I had to create a new origin account and online support generated a new key for that new account.
So I would be really cautions about using a key from one of these sites. If you do I would advise creating a Origin account Just for the game so that if you key/account get disabled it won't affect any other origin games you have.
I'm not sure about Premium specifically, but I know someone who bought an Russian version of the game; beyond having to download a language pack, they had no problem running it. However some games will check your locality when installing, or may have region-specific keys (as you have considered).
I doubt the key is region specific, but you never know. Plus there is always the possibility that they could retrospectively enforce this later, which would be infuriating.
However, I'd completely recommend you don't buy Premium from Origin. I bought a boxed key version for 20% less (£33 vs £40), which is a decent saving for a 2 day wait.
By all means, buy a grey-market version - there is a decent chance that it will work, However, be prepared to suck up the consequences if it doesn't. To quote Clint:
You've gotta ask yourself a question: "Do I feel lucky?" Well, do ya, punk?