Reader Barry Midgorden suffers from a slow Internet connection and wishes to eliminate a redundant download. He writes:
I live in a rural area where my Internet service options are limited and slow. My wife and I both have iPhone 3Gs and now want to update to iOS 4. We each have our own Macs with our own iTunes libraries and accounts. I’ve downloaded and installed iOS 4 on my iPhone, but it took hours to accomplish. Is there a way to update my wife’s iPhone using her Mac and iTunes by transferring some installer package from my Mac to hers so we don’t have to download the iOS 4 update again?
There is. The file you need is on your Mac. Follow this path: youruserfolder/Library/iTunes/iPhone Software Updates. In this folder you’ll find an iPhone restore file (ending in .ipsw) dated sometime in late June 2010. Copy this file to your wife’s Mac. Although you needn’t copy it to the same location, doing so will make it easier to find the next time you need it.
Now launch iTunes, select the iPhone in iTunes’ Source list, hold down the Mac’s Option key, and click the Restore button. When you do, a Choose a File: iTunes window appears. Navigate to the .ipsw file, select it, and click the Choose button. iTunes will verify this file with Apple over the Internet. This is a short check to make sure the file is the real deal—iTunes won’t download another copy of the installer file. Once iTunes is satisfied with the file, it will use it to update your wife’s iPhone.