1. Make sure you have the latest iTunes version, at least iTunes 8.
2. Synchronize your iPhone with iTunes.
3. Connect your iPhone to iTunes and backup your iPhone to seperate file. This backup will be copied to rented iPhone and later will be used to restore your iPhone.
4. Connect rented iPhone to iTunes and when it shows up in devices click on it and then right click on it and choose Restore from backup. Then iTunes give you options which backup to restore from, choose the one you did in previous step. It will restore all settings, though it will not yet restore all content you had on your iPhone.
5. Your rented iPhone will show up in Device section in iTunes with exactly the same name as your iPhone. Click on the name and change it back to its original name (choose one). This way iTunes will make backups of rented iPhone and will not mix up with the backups from your iPhone.
6. Choose synchronize options in iTunes and click Apply – it will copy all content from your iTunes library (including applications) to your rented iPhone. Now your rented iPhone has the same name and settings as your iPhone.
7. If you travel with rented iPhone abroad and want to use unlimited 3G internet, (the service provided by KeepGo.com), specify in rented iPhone settings all configuration details of your abroad cellular carrier (these details provided to you by KeepGo.com). Now you are setup and ready to go.
You can copy all your content and settings from your iPhone to the rented iPhone using the steps shown in the video below: