Why do get SMS send to the wrong recipient ( HTC Thunderbolt)?
There are many people facing similar problem here, http://community.htc.com/na/htc-forums/android/f/107/t/12961.aspx?PageIndex=3

The solutions they came up with was:


Use handcent SMS app instead of stock SMS app
Keep low number of messages in inbox
Delete read message
Waiting for Gingerbread update which will fix it


If I were you I'd choose number 1.