Can you send? Also, did you just get your device / account? If yes, something during setup could be missing. I'd speak with T-Mobile Customer Service...
I did speak to customer service. They made me sent a text message. Everything seems ok on my screen. It even show me a check mark. The rep. told me, it means the message went trought. Then I called my friend. She did not received the message. and she also send me one text mess. I did not received either.
Thanks for your help