Straight Talk doesn't permit Sprint BYOP's at this point in time, and trying to SIM unlock the GSM radios on it without Sprint's permission is currently against federal law. That hopefully will change in the near future, but that's the way things currently are. Have you tried looking to see if Virgin Mobile or Boost Mobile will allow you to bring your HTC One to them? I know at least one of them have BYOP for Sprint devices to my knowledge.