1. Press Menu

2. Tap Settings

3. Tap Wireless and Network

4. Tap Mobile Network

5. Tap Network Operators

6. Tap Search Networks

7. Tap any Network other than your own service provider (device will show "Your Sim  Card does not allow a connection to this Network") 

8. Tap Ok

9. Tap your own service provider's network after the list is refreshed.

10. Press the Home Button