I am of two minds concerning this incident.
You are so quick to call her "white trash", but what about your brother who is not even divorced yet? I wouldn't call knocking up a 19 yr old to be the most stellar behavior either. Maybe they didn't call you because you hate the girl. If you were my SIL or FSIL, I probably wouldn't have called you either.
I do, however, agree that it is really not a good situation and you should have been told in person. You do have a right to be hurt here.
As far as your baby's things, no one has a right to them. You have the right to give them to anyone you want to give them too. Your brother has the responsibility, along with his girlfriend, to provide for their own child. I also was expected to hand everything to a niece who kept getting knocked up. I absolutely put my foot down the third time and said no.
However, if you are giving them away anyway and you don't have anyone to give them to, perhaps you could give them a few things. This is going to be your niece/nephew, even if you hate the mother. You really might want to consider being nice to her or at least civil, especially if you are interested in seeing the child. Because people who are hateful to me don't see my children, no matter if they are "family" or not.
I really do understand your feelings, though.