I couldn't get Apple's configuration tool to work for me. I tried the Tmo swap trick too, but that didn't work either.
What I learned DID work was just popping the SIM out, going to the settings screen, popping it back in, doing the app change trick, and then changing the settings as needed.
Basically, follow http://wiki.howardforums.com/index.php/Straight_Talk_iPhone#... but don't use a T-Mobile sim card, just pop the ST one back in.