Download iOS Updates Once for Installing on Multiple Devices

If you have several iPhones, iPads, or iPods that need updating to the latest version of iOS, you can use a nice trick to save some bandwidth and download a single iOS update file to apply to multiple devices from either Mac OS X or Windows. This is a perfect solution for a family that has multiple iPhones or iPads that need updating, particularly when you don’t want to download the same firmware multiple times.
To be clear, the iOS devices must be of the same type and model, meaning three different iPhone 4s can use the same firmware, but an iPhone 4 can’t use the same update file as an iPad 2 would, and an iPod touch can’t use an iPhone 4S update file, and so on. Same models use the same IPSW, different models need different IPSW.

How to Use a Single IPSW File with Multiple iOS Devices

To do this, you will need to download the iOS firmware files directly from Apple. Here are firmware links for iPad, iPod touch, iPhone if needed, once you have the file you place them into the folder where IPSW files are stored locally. Here’s the process for Mac OS X and Windows, and yes you can use an IPSW file downloaded on a Mac or PC to update an iOS device connected to a different PC or Mac, the files are platform agnostic.
For Mac OS X:

1. Quit iTunes
2. Hit Command+Shift+G to bring up “Go To Folder” and enter the following path, depending on your iOS device:
~/Library/iTunes/iPhone Software Updates ~/Library/iTunes/iPad Software Updates ~/Library/iTunes/iPod Software Updates
3. Drag and drop the downloaded IPSW file into the appropriate location
4. Launch iTunes and connect the iOS devices to the computer to initiate the upgrade

For Windows:

1. Quit iTunes
2. Use Windows Explorer to navigate to the following directory, depending on the iOS device and version of Windows:
Windows XP: \Documents and Settings\username\Application Data\Apple Computer\iTunes\iPhone Software Updates Windows Vista & Windows 7: \Users\username\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates
3. Move the IPSW file into the appropriate Software Updates directory
4. Relaunch iTunes and connect the iOS device to the PC

That’s all there is to it, and here’s how it works; anyone can download the updates without iTunes by using direct firmware links from Apple’s servers. Once you have the firmware file you can either use the standard method of using .ipsw files with ALT/Option clicking Restore, or use the approach outlined above which fools the computer into thinking it downloaded the iOS update itself, which will then immediately unpack and start the iOS upgrade process upon the launch of iTunes.
Don’t forget about OTA updates either, which allow iOS to download and update only the changes between releases. The resulting OTA update can often be 1/12 the size of a full firmware file, and although they can’t be shared between multiple devices the small size of the on-device update can make it a valid choice for the bandwidth conscious.