My iphone isn't working in the Philippines?

Hello,

My sister has an iPhone 3GS that she got from a friend. We submitted an unlock request on the AT&T website and followed the emailed instructions. Somewhere I read that when I restore from a backup, it will say something like, "congratulations! Your iphone is unlocked!", but we got no such message. I checked it on iphoneimei.info, and it said it was unlocked, so she left for the Philippines a week ago. When she got there, she tried putting a local SIM card inside her iPhone, and it said "invalid sim". She knows that the sim works because she can use it in a local phone there. She went to an apple store there and they confirmed that the iPhone was unlocked. Any suggestions would be appreciated!

Thanks!

-Mark