I don't think T-Mobile gave away any of our info... some peoples' posts say something like "Hi [First Name]" which is kind of like the text message is asking our phone to put in your first name... I think Android phones will actually put your name into the message.
These seem like someone who is trying to play pranks or maybe even learning to "phish" information from people. Better if you DO NOT reply.
If they're just trying to figure out what phone numbers are real, they could be getting the "delivery receipt" and just writing down which numbers actually receive the message. If you reply, they might get more info from you (don't fall for an identity theft). Keep in mind they could also read this discussion, so don't post anything too personal or detailed here.
I also got a spam SMS from this number, and it auto-inserted my first name.
Just so you all know, you can report spam to T-Mobile by following the directions here: http://support.t-mobile.com/docs/DOC-2747
Make sure you only send the phone number when the system replies to your forwarded message... For example:
1. Forward the spam text message
2. Receive a reply saying "thanks for reporting Spam, please reply with the sender's number"
3. Reply "4042002194"