The Sprint Samsung SPH-A900 does not allow users to upload their own ringtones onto the phone by default. In order to get around this problem, special software must be used to browse your phone's file system. Additionally, special files must be placed along with the ringtone in specific directories located in the phone's file system.
STEP ONE: THE MSL NUMBER
This is probably the most important step in the process. Without getting the MSL number for your phone, everything else on this site is useless.
The MSL number is a code specific to your phone, and is generated by your carrier (Sprint). Unfortunately, I can help you the least with this step. You have to call customer service and specifically ask a rep for your MSL number.
UPDATE: Check out this thread on sprintusers.com to obtain your MSL without calling Sprint. I tried this method and it worked for me. You'll need CDMA workshop.
STEP TWO: USB DRIVERS
If you've never connected the phone to your computer before, download the USB drivers found in the drivers tab at the top of this page. Unzip the files to a folder. When you plug in your phone using the data cable it came with, windows will ask to "install new hardware." Point it to the drivers directory you just unzipped. It needs to do this twice. I believe once for the USB drivers, the other for the modem drivers. After this is done, restart the computer.
STEP THREE: QPST
QPST is software created by Qualcomm to manipulate files on mobile phones. Download the program found in the drivers tab at the top of this page, then install it. Connect your phone to the computer using the USB cable. Start up QPST and click the "ports" tab. Click "Add new port." This is the COM port used when you set up the drivers in the previous step. To check what port this is, go to Device Manager, under modems, and you can look up what port the Samsung modem uses. It's usually "Com3" or "Com4." It was COM15 for me, and it's changeable in Device Manager. Once your phone shows up in the Active Phones field click the "Start Clients" menu and click "EFS Explorer"
Enter the MSL number in the SPC field and you're in! EFS Explorer will browse and display the file system of your phone. As a word of caution, this contains all the stuff that makes your phone work. Please be careful—don't delete stuff unless you know what you're doing.
STEP FOUR: PLACING THE FILES
in the EFS Explorer in QPST, browse to the following directory:
/brew/mod/obione/jas/index/
In there you'll find a bunch of .txt files. These files are references to all the custom files on your phone. 1.txt and 2.txt are OnDemand and Sprint Music Store, along with other demos. The key here is to look at what numbers are being used by your phone. When you want to create a new ringtone, you'll have choose a number that is not already in use. While the number does not have to be sequential, it does have to be unique. I usually make it sequential though.
Now that you've noted what number you want to use for your new ringtone, click on the Upload tab and upload your ringtone on a900hack.com! Put the number that you've chose in the "internal song number" field. The application will kick back 3 files. Download them all, and place the .txt file that is generated in "/brew/mod/obione/jas/index/" folder using EFS Explorer.
Now, what about the other two files? The .gc and .gcd files need to be uploaded to the phone as well, but in a different folder. They will go in the following directory in EFS Explorer:
/brew/shared/jas/content/
You can repeat this process if you want. When you're done, you need to reset your phone. QPST has a "reset phone" button. When your phone resets, unplug the USB cord from it. Once the phone has booted back up, go to the Ringers. Your new ringtone should be there with the name you gave it in the upload form. Congratulations!
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