Why won't my T-Mobile micro SIM not work on iPhone 4 ?

I bought an iPhone 4 ( and bought the unlock off ebay) and went to T-Mobile and got myself a Micro SIM for it.
Then i Called t-Mobile Support, changed my SIM and Activated my Micro SIM..
The Represenative said it should take 10min up to 2 HOURS for the SIM to be up and running.
I Rebooted my Device and shut off my Wi-Fi, the Internet works, but Calls and MSG Dont.
When i have my brother call my Phone, it would go straight to Voicemail as if it was still the old one.

-When the phone is on it shows the "T-Mobile" Carrier, Bars, and the "3G" sign.