When you have the list of the people who have texted you. The person you want to black list in that list. Hold down their name. A box will pop up. scroll down that list (it's longer then the window itself) and you will see blacklist.
Lately. I get a few issues. Sometimes I get a notificiation that I have a new text , when i pull down the status bar, it directs me into handscent app which shows no new texts in any threads.
the other issue, is sometimes I get a new text, read it in the pop up window, close the window and it does NOT put that text into the thread or anywhere that I can re read the text. Extremely frustrating as sometimes the whole text is too big for the pop up and when u try to read the whole message from the app... its not there.