Follow these steps to enable the AWS bands (the bands used by T-Mobile for 3G/4G HSPA+) on your AT&T Galaxy S3 SGH-i747 and receive 3G/4G HSPA+ data when using T-Mobile SIM card.
- Download the T999L NV Data backup file from HERE.
- Download and install QPST from HERE.
- Dial *#0808# on your phone to access ‘USB Settings‘ and select ‘RNDIS + DM + MODEM‘ and press ‘OK‘.
- Connect your phone to your computer via USB. You should see some kind of ‘SAMSUNG Mobile USB Serial Port‘ under ‘Ports‘ in Device Manager.
- Start ‘QPST Configuration‘ and click ‘Add New Port‘ under ‘Ports‘ tab.
- Uncheck the ‘Show Serial and USB…‘, and select the COM port you saw earlier in Device Manager, and click OK.
- Click the ‘Start Clients‘ menu at the top and choose ‘Software download‘.
- Choose ‘Backup‘ tab, then choose your COM port, and set QCN file name and hit ‘Start‘. This will backup your current NV memory. If something goes wrong, you can always restore the original NV memory.
- Choose ‘Restore‘ tab, choose the QCN file ‘T999LNVData.qcn‘ you downloaded earlier and hit ‘Start‘. This will flash the new QCN file with AWS bands enabled. If QPST says that it failed to restart your device just reboot it yourself manually.
That’s it! If you are using T-Mobile SIM in your AT&T Galaxy S3, you will see that it picks up HSPA+ signals just fine.
If dialing ‘*#0808#’ doesn’t work on your phone, you can download and install the phone utility app ‘phoneutil.apk‘ by following these steps:
- Open the browser from your phone and type in this URL:
and download the ‘phoneutil.apk’.
- If you can’t install the utility app, go to ‘Settings‘ => ‘Security‘ and check the ‘Unknown sources‘.
- Now instead of dialing ‘*#0808#’, dial ‘*#7284#‘.