Ok this is odd. I'm on Verizon and got that same exact text mssg you did. It started about a hour after it was activated and I received it twice each hour in 30 minute intervals. Probably got that text 15 times more or less. I called Verizon and they said to text back "stop" or "cancel" or "unsubscribe". I did this about 4 times and it FINALLY stopped.
Spam is not your problem. You must of had been on a regular phone before you switched to your blackberry. It has to do with your mail settings on your providers side. You will need to tell them that you are getting Brew messages and a good rep ot tech will no what you are talking about. They will get it fixed for you. It usually happens when you switch phones non blackberry to a blackberry. They didn't cancel your mail box on the other phone. Trust me call customer service and they shoud get you set up over the phone in mins..