Can I apply my iPhone 3GS backup to my iPhone 4S?

Solution 1:

To restore from backup

• connect the iPhone to your computer
• wait for it to appear in iTunes
• right-click on the iPhone listed under Devices and select "Restore from backup..."
• select the backup you want to restore (there may be several)

Restoring will only touch user-specific content and configurations.

Solution 2:

You can restore pretty much any iPhone backup onto any other iOS hardware.

Should you have made some settings changes for hardware that is no longer there, those will sit there unchanged and hidden until you restore that backup back onto a device that can use that setting.

You also don't have to worry about being hobbled - the software was designed to let you use all the new features even if you bring an older backup. The device will give you the new default settings for items that are absent in the old device.