What data does the Carrier IQ daemon log from iPhones?
It appears that very little, and it can be completely disabled.


  Carrier IQ, the now infamous “rootkit” or “keylogger”, is not just for
  Android, Symbian, BlackBerry, and even webOS. In fact, up through and
  including iOS 5, Apple has included a copy of Carrier IQ on the
  iPhone. However, it does appears to be disabled along with diagnostics
  enabled on iOS 5; older versions may send back information in more
  cases. Because of that, if you want to disable Carrier IQ on your iOS
  5 device, turning off “Diagnostics and Usage” in Settings appears to
  be enough.
  
  http://blog.chpwn.com/post/13572216737