I have unlocked my LG Thrill 4G and I'm using it at Brazil, I use the carrier called "Oi" It works perfectly for 3months and when I took off my sim card off the phone and put it back on it shows "No sim card".. I'm thinking it's because it can't read it or something, I actaully have 2 LG Thrill 4G And I tried with my other one (Also unlocked) It shows the same message.

Anyone can help me?