How to know my iPhone 3G is unlocked?

My buddy put the IMEI through an unlocking system and said it should be complete by the end of the day or first thing tomorrow morning. How do I know when it's unlocked? It was an AT&T phone then we bought a SIM card for T-Mobile. Will it just say T-Mobile where it says No Service right now? Anything will help!

When the unlock has been completed, provided the sim for T-mobile has been activated, you will see the signal strenghth icon T-mobile 3G across the top of the screen.

If the new sim is active but the unlock hasn't been completed you'll see the roaming icon instead of 3G, or you may just get 'inactive sim card' across the centre of the screen.