I have an iPhone 4 that I recently requested an unlock for (and was approved). I would like to update it to iOS 6 so that iMessage at least works. But I don't want to slow it down with iOS 7. So I found a few sites to download iOS 6.1.3 and in iTunes, I hold down option while I click restore. I select the IPSW of 6.1.3 and it goes through the motion until I get an error stating that "The iPhone could not be restored. This device isn't eligible for the requested build." Do I HAVE TO upgrade to iOS 7? Am I missing a step? Any thoughts? FULL DISCLOSURE: This was jailbroken and used in Asia for about a year. I also tried "erase all content and settings" and that doesn't work.