If anyone would like to try iOS 7 on their GSM iPhone 5...
It seems as if Apple forgot something important in this version of iOS 7 for the GSM iPhone 5. It doesn't check to make sure if your UDID is registered with Apple's developer program. So that means that you can try iOS 7 for yourself!
Steps for iOS 7:
1) Plug in your iDevice into iTunes and backup to your computer, not iCloud. Don't forget to click Sync as well! The backup is in case something goes wrong.
2) Head over to https://imzdl.com/ios.php and find your device's download and download from the right side.
3) The page will redirect to another site for the download. Don't worry, the download is secure and safe.
4) After the backup is complete (check and make sure that your device backed up by looking under that backup options in iTunes where it says "Last Backed Up on:") and the download is complete, locate the downloaded file on your computer so you know where it is for the next step.
5) Update time! In iTunes, Shift + Click on the "Check for Update" button (for Mac, Option + Click). A window will open up for you to find and select the downloaded file from Step 3. Select that file and hit "Open."
6) Let iTunes do it's thing and update your iDevice to iOS 7!