A minor and perhaps irrelevant point, but AA does not send text messages. They send an email to your phone number that comes to you in the form of an SMS.

Some providers (T-Mobile for sure) allow you to create filters on their website for these emails received as SMS messages. As I am now a BlackBerry user, I have these routed to my GMail account so I do not have to pay the SMS charges...and still get the messages just in case they are legit. Since I've done this, I've not received (nor paid for) a single spam SMS.