If you have a Nokia Lumia 900 with AT&T and travel frequently, we have good news for you. WPCentral discovered that you can now call AT&T to unlock the device so you can use SIM cards from other carriers. You’ll need your IMEI number before calling.
Some people had their Nokia Lumia 900 unlocked easily, but others did not have the same luck. Results may vary.
To obtain your IMEI, dial *#06# or go to Settings > About > More Info.
Another commenter suggested live chat to unlock your Nokia Lumia 900.
Go to att.com/wireless, go to support, you will need to log in to do a live chat. pick international live chat, say you want to unlock for international use. Verify account, give IMEI, they will provide you with a pin.
I am all set, it should be pretty easy. Dont answer more than you need. that always help.
Have you been wanting to unlock your Nokia Lumia 900? Try the steps above and let us know if it worked out.