[AT&T Galaxy Note 3 General] najoor:
[Guide] How to switch from AT&T to T-Mobile and keep your SM-N900A fully functional

** DISCLAIMER: I AM NOT A DEVELOPER. I DO THIS AS A HOBBY AND SHARE MY FINDINGS IN CASE SOMEONE ELSE FINDS THEM USEFUL. **

** THIS WORKED ON MY DEVICE BUT IT MAY NOT WORK ON YOURS. APPLY AT YOUR OWN RISK **​

Background

I always hated AT&T. When I got my first US cell phone in 1998, AT&T was a dominant force and Cingular was the underdog that provided better service. So for years I went out of my way to keep it Cingular through all of my relocations and phone number changes. Then AT&T bought Cingular and I was forced to become an AT&T subscriber. Then the iphone came along on the AT&T network, with the unlimited internet plan, which sealed my fate with this carrier for years.

At some point AT&T stopped offering the unlimited plan and I was one of the lucky ones who had their iphone plans grandfathered in. That prevented me for a long time from switching, but it became increasingly clear that AT&T has no intention of letting me use my plan as intended. All the signs were there: from threatening text messages every time I tried to tether my phone, to insulting slow-downs of data transfer after 2-5G of usage. At some point one gets tired of feeling like a criminal who is constantly trying to trick the carrier to squeeze a little more service here and there.

The last straw was when they made it very clear that they will not allow me to use a tablet as a phone, even if it has phone capabilities, even if I let go of my unlimited data plan! Their solution? buy a new data-plan only for your tablet. I am done with this $#(^. T-mobile had me at hello. All it takes is to notice the choice of music they play for you when you are on hold with the customer service: ATT: elevator music, T-mobile: Miley Cyrus.

So, here is what I did to make the switch and keep my note 3 issued by AT&T to use on T-mobile network.

Why?

If your phone is unlocked you can certainly pop the new sim card in and it will latch on to the T-mobile network. However you will be missing all the goodies that come with a T-mobile issued phone. Hence my journey to T-mobilize my SM-900A. A T-mobile Note 3 has an unlocked bootloader. I cannot have that transferred to an AT&T phone. But there are other good things that can be ported over. For example T-mobile's WiFi calling is implemented at the OS level and you cannot just copy over an APK to make it work. So if you follow this guide you will be able to turn your phone on and boot it up to (almost) exactly what a SM-N900T looks and behaves like.

Requirements:

1- Your phone should be on Jelly bean 4.3. Mine was on N900AUCUBNB4 but lower versions will work too. I have no intention of upgrading my phone to Kitkat anytime soon because I simply do not see the advantage. However, an experienced developer should be able to modify this process for Kitkat.

2- Your phone should be rooted.

3- You will need about 5G of empty space to install the T-mobile ROM.

4- Read the instructions below once before you start anything. If any word or phrase does not make sense to you STOP, google, ask questions, make sure you understand it, then continue.

Instructions:

1- Always backup your important stuff before doing a thing like this to your phone.

2- Root your phone if it already isn't. Your options that won't trip knox are Kingo and Towelroot. I recommend the latter.

3- dwitherell has done a great job of preparing a Jelly Bean T-mobile Rom for porting to AT&T. Download TweakedN3v2.0.12614 from http://xdaforums.com/showthread.php?t=2625946

4- This ROM is pre-rooted but contains a few things that should be removed or tweaked for our purpose. Unzip it somewhere.

5- Delete vrtheme directory and bootcolx.img and bootstock.img

6- Replace defaults\install.prop with the file attached below.

7- Replace META-INF\com\google\android\updater-script with the file attached below.

8- Re-zip the whole thing again and call it N3-Tmobile.zip (or whatever you want)

9- Copy that to your sdcard. It may also be a good idea to copy a file manager apk like "File Manager HD" on your sdcard as well so you can later install it when the T-mobile Rom is in place.

10- Install Note 3 AT&T Safestrap 3.71 for Jelly Bean on your phone. It can be found at: http://xdaforums.com/showthread.php?t=2572978

11- Boot into Safestrap recovery and create a Rom slot. Call it T-mobile or whatever you like. Activate it.

12- From the Safestrap main menu, install the N3-Tmobile.zip that you created in step 8 into the T-mobile slot. Be careful not to mess up your Stock Rom slot. The installation may take 3 to 10 minutes. If it takes longer, reboot the phone, wipe this Rom slot and try again.

13- When it is done, go to Safestrap main menu -> wipe -> advanced wipe -> select ONLY Dalvic, data, and cache, and the hit the wipe button.

14- Turn off the phone. Take out your AT&T sim card out, DON'T put your T-Mobile sim card in yet. Turn the phone on and reboot to the T-mobile Rom. Don't enable Wifi in the initial setup.

15- Now your T-mobile Rom is up and running but you don't have internet or cellular connections.

16- In your /system/app directory rename the following to [file_name].apk.bac (this is where the second part of step 9 becomes useful):

FotaClient.apk

FWUpgrade.apk

LocalFOTA.apk

SPPPushClient_Dev.apk

SyncmlDM.apk

16- Turn your phone off, put the T-mobile sim in it, turn on and enjoy.

If you want to swap the sim card back to AT&T, all it takes is to reboot to your stock ROM. Everything will be still there as you left them.