[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] ibanezbass:
I've noticed several users having trouble with their phone when editing the build.prop. They will edit the file, reboot, anxious to use Google Wallet, and be greeted with a black screen of death. Their heart will jump in their throat and they think... "Oh no... I didn't nandroid backup... What's a nandroid backup anyway?" No worries! I have the solution for all of you. Hopefully this short guide will get you going again.

I'm going to run through a quick setup of the Android SDK so that you can use adb if you choose to go this route. The SDK will be useful all though rooted phone usage, so I suggest you download it and use it. ADB is a very powerful tool. First, Google Android SDK. The first result should be the official site for the Google developer section. Just open that top link and the page should have a huge button that says "Download the SDK for (Windows or Mac or whatever)". Click it. Mac users.. Yours does not actually setup. You need to find the SDK Manager app within that zipped download and run it. Windows users... Run the setup. When it's done it will open the SDK manager. Both Users... Check the box next to the "Android SDK Platform-tools". Bottom Right, Install x Packages. Make sure you take note of the SDK path displayed at the top of the manager. EG. C:\Users\Josh\AppData\Local\Android\android-sdk. Mac users: Yours will be in the downloaded folder that you extracted. All Users: Navigate to that folder via terminal (mac) or cmd.exe (windows). Windows: cd C:\Users\Josh\AppData\Local\Android\android-sdk ... Mac: cd /Users/josh/Downloads/android-sdk/ ... Then navigate to the platform-tools folder that is within the SDK folder. Here is where ADB is located.

You also need the naked ADB drivers if you're a Windows user... Here http://xdaforums.com/showthread.php?t=1379875

Once you reboot your phone into recovery: Open start menu, right click on Computer, click properties. This will open the system panel. Top left, click device manager. Somewhere along there, see if you see your device name (something like "Samsung-SGH_I747") with an exclamation point or question mark. Double click it if it does. Click update driver in the window that opened. Click "Browse My Computer...." "Let me pick..." "All devices / next"... "Browse". Now go find where you downloaded and extracted the naked driver zip. Open the folder and double click on one of the available .ini files. You'll get some compatibility warnings, just continue.

Windows instructions:

Download adb.exe, either through the Android SDK or elsewhere. Use Google.

Connect phone to computer via USB.

Boot phone into recovery.

Use cmd.exe (Use Windows key+R, and type cmd in the run window) to navigate to the folder containing adb.

E.g. "cd c:\Users\Josh\Downloads\adb"

Run "adb shell"

This should initiate a shell to the phone allowing you to run commands on the phone. If you get an error, make sure you have the drivers loaded for your phone.

Run "cd /system"

Run "chmod 644 build.prop"

Optional: Run "ls -l" and make sure that the permissions on build.prop show RW-R--R--.

Reboot phone.

Mac Instructions:

Download the adb application, either through the Android SDK or elsewhere. Use Google. Make sure you download the Mac version, not the Windows or Linux version.

Connect phone to Mac.

Reboot phone into recovery.

Open Terminal on Mac. /Applications/Utilities/Terminal.app or use spotlight to find it.

Navigate to folder containing the adb app. E.g. "cd /Users/josh/Downloads/adb/"

Run "adb shell"

This should initiate a shell to the phone allowing you to run commands on the phone.

Run "cd /system"

Run "chmod 644 build.prop"

Optional: Run "ls -l" and make sure that the permissions on build.prop show RW-R--R--.

Reboot phone.