title: iphone programming objective-c : track user location in background questions
body: <p>i have read that we can track user location in background. 
  I have put in plist backgroundmodes array = location. 
  I want to know if this only work with iphone 4 and 3gs?
  Also , when the user change location while in background, does it triggle the DidFindPlacemark method? </p>
  
  <p>finally is there a tutorial with "CODE" somewhere or a sample for this thing?</p>
  
  <p>thanks</p>