[Sony Xperia Z Ultra] Riza:
Thanks to blueether for His very useful thread

! ATTENTION !

There is a SIMPLE SOLUTION HERE

The C6833 modem works for my C6802 [TESTED]

Thanks to Triflot​

Requirements:

*. DO IT AT YOUR OWN RISK, I'M NOT RESPONSIBLE FOR ANYTHING THIS WILL DO TO YOUR PHONE

1. Xperia Z Ultra (Absolutely! :p ) [Tested on XZU with Unlocked Bootloader]

2. FlashTool, Download link & tutorial here

3. Required FTF (NUT's *.532 & *.136)

4. Custom ROM

5. PC running Windows OS

How to get into Flash Mode:

1. Power Off your Z Ultra

2. Press & hold Vol-

3. Plug your phone to your PC (USB driver > read for intallation step here)

How to get into FastBoot Mode:

1. Power Off your Z Ultra

2. Press & hold Vol+

3. Plug your phone to your PC (USB driver > read for intallation step here)

[TRICK] Get Into FastBoot Mode/Flash Mode​

If you're having trouble getting into FastBoot Mode/Flash Mode, you can try this trick

1. You have to be on Windows

2. Make sure you opened FlashTool & installed driver for Z Ultra

3. Open Device Manager

4. Show hidden device [Not really necessary, I did this to make sure my Z Ultra driver is installed]

5. Plug your phone while holding Vol+ (FastBoot) OR Vol- (Flash)

6. If it doesn't recognized by Windows, then Scan for hardware changes (this simulate USB Unplug & Replug for me), do this while holding the Volume Rocker

7. Repeat number 6 until you got it connected

For Windows 8/8.1 Only:

When you connected Z Ultra using Flash Mode to your PC, it'll disconnect after a while, to solve this problem, try to prepare your files you want to flash first, then when FlashTool asked to connect your phone, do step 1 to 7, your phone won't disconnect at the time it being flashed

Fresh Install [RECOMMENDED]​

Steps:

1. Flash NUT's Modified *.532 STOCK ROM Using FlashTool [Default Settings, Flash Everything]

2. Flash extracted boot.img file from CUSTOM ROM You Want To Install via FastBoot Using FlashTool

3. Boot Into CWM/TW Recovery

4. Flash CUSTOM ROM + GAPPS via Recovery

5. Flash Custom Kernel Here If You Want To Use It, If Not, Then Go To Step 6

6. Reboot Into System You Just Installed [IDK If This Is Necessary]

7. Reboot To Flash Mode

8. Flash ANY *.136 STOCK ROM Using FlashTool

Settings:

[Wipe] Data	: Unchecked

[Exclude] Kernel	: Checked

[Exclude] System	: Checked

9. Reboot, Hopefully IMEI and BASEBAND Will Be Available

Thanks to x1123 for his post here

Update Custom ROM [EXPERIMENTAL]​

*Please Correct Me If I Wrong

Steps:

*. This Will Not Keep Your Google Account, So, Contacts, Mails, Hangouts Messages, etc. That Related To Google Account Will Disappear

1. Flash NUT's Modified *.532 STOCK ROM Using FlashTool

Settings:

[Wipe] AppsLog	: Unchecked

[Wipe] Cache	: Unchecked

[Wipe] Data	: Unchecked

2. Flash extracted boot.img file from CUSTOM ROM You Want To Install via FastBoot Using FlashTool

3. Boot Into CWM/TW Recovery

4. Flash CUSTOM ROM + GAPPS via Recovery [GAPPS Must Be Installed, Otherwise Google Framework Will Crash]

5. Flash Custom Kernel Here If You Want To Use It, If Not, Then Go To Step 6

6. Reboot Into System You Just Installed [IDK If This Is Necessary]

7. Reboot To Flash Mode

8. Flash ANY *.136 STOCK ROM Using FlashTool

Settings:

[Wipe] AppsLog	: Unchecked

[Wipe] Cache	: Unchecked

[Wipe] Data	: Unchecked

[Exclude] Kernel	: Checked

[Exclude] System	: Checked

9. Reboot, Hopefully IMEI and BASEBAND Will Be Available [Some Google Apps Will Disappear, You'll Need To Re-Install It]

Tested ROMs: copied from here

Carbon - Build 8: Working

SlimKat: Not tested yet

LiquidSmooth: Not tested yet

FXF CM11: Not tested yet

CM11: Working

AOSP: Not tested yet

AOKP: Not tested yet

AICP: Not tested yet

Lungo: Not tested yet

PAC-man: Not tested yet

PA: Working

Chameleon OS: Not tested yet

GPe ROM: Not tested yet