Unlocked Iphone 4 still can't read some simcard?

I bought my iphone 4 directly from apple in the uk, and it was already unlocked/free from any carrier. It works fine with my italian Tim simcard but it does not work with my Brazilian Tim nor Oi simcards… Any ideas?

It will not work with some networks outside the EU and there's nothing you can do to get it t o work.

Try send your device to Apple shop. Why don't you upgrade to the Iphone 5. You can get it for free here
http://www.iphone5contest.info. I already got it last week. It is better than iphone 4/4s

If you bought it from the UK it's set to read UK sim cards, or at least those from europe, it sounds to me that it needs activating though, have you spoken to the carrier of the sim thats not working? Another thing with the iPhone is it will lock to the network of the first sim you put in it when it comes out of the factory, I would start by speaking to apple, they are very helpful and will know exactly what's going on.
Hope this helps
-em86