[T-Mobile LG G2x] xBkKx:
These steps are mainly directed at how to use the KDZ program to switch your baseband/fixing unknown baseband.

*I have heard this works on Windows Vista/7 but I personally have only been able to accomplish it through Windows XP*; VMWare running XP and XP Mode also work but make sure the USB is consistently being connected to the XP environment (don't jack around outside it) or the process will hang & require you to start over!*

1. You do NOT need to have stock recovery installed for this to work, it will require you to reflash CWM after though - How to NvFlash CWM Recovery

2. If you are not on a stock ROM prior to doing this your phone will get stuck in a boot loop of the stock T-Mobile animation when the process is finished; until you reflash CWM Recovery and restore a backup

Notes:

[

While on a custom ROM and Recovery]

I have had the kdz method hang after the baseband flash but before installing the stock ROM & Recovery, leaving everything but the baseband unchanged; this could happen for you but I recommend making an Nandroid still if you care about losing your current data; similar log of how it will appear if this happens: Baseband flash hangup

[Modem causing process to hang]

The process may hang due to the LG Modem driver, disabling and re-enabling it should fix this (Start --> Run --> devmgmt.msc --> Modems --> LGE Android Platform USB Modem --> Disable/Enable)

Needed files:

T-Mobile G2x Android USB Driver - drivers so your computer recognizes phone

V11H_00.kdz | Mirror 1 - data for the June 05 2011 baseband (WIND MOBILE)

V21E_00.kdz | Mirror 1 | Mirror 2 - data for the July 15 2011 baseband

V21Y_00.kdz | Mirror 1 | Mirror 2 - data for the March 11 2012 baseband

KDZ_FW_UPD_EN - software to install the baseband

APX Drivers & NVFlash - driver and software to flash Clockwork Recovery on your phone again

P999 V10F Nandroid - Nandroid of stock 2.2.2/V10F ROM

P999 V21E Nandroid | Mirror 1 | Mirror 2 - Nandroid of the stock 2.3.3/V21E ROM

P999 V21Y Nandroid | Mirror 1 | Mirror 2 - Nandroid of the stock 2.3.4/V21Y ROM

LGMobile Support Tool - Checks if the LG ROM/Baseband is outdated

Call audio fix for V21E Baseband | Mirror 1 - Fix the audio issue during a call with the V21E baseband on a custom ROM

Call audio fix for V21Y Baseband | Mirror 1 - Fix the audio issue during a call with the V21Y baseband on a custom ROM (So you can still be on CM9 nightlies thanks to owain94)

If you're trying to update from the V21E/July 2011 baseband to the V21Y/March 2012 baseband you should only need the LGMobile Support Tool and be on a stock 2.3.3 ROM to get the new baseband.

Download whichever file(s) you need from above; if you've been crack flashing with your computer already you should only need the KDZ program & the V21E/V21Y baseband file

Install the G2X driver onto your computer

Extract the KDZ_FW_UPD_EN archive and right click the "msxml.msi" file and select Install

Next keep your finger held on the Volume Down button of your phone and connect the USB cable to the phone and computer and wait until your phone displays "S/W Upgrade; if your computer says it detected a device it needs a driver for extract the APX/NvFlash zip and navigate the computer to the APX folder for the driver"

Open the "KDZ_FW_UPD.exe" file and click the folder icon to locate the KDZ file

After you have navigated to the KDZ file select it and push "Launch software update"

The log will instantly show:

15:54:41 : Launching SW update
15:54:41 : Unpacking KDZ

*The program will hang for a minute or two while it is unpacking the file don't worry!*

After you will see some information similar to this:

15:54:51 : KDZ file extraced
15:55:08 : Files were extracted.
15:55:08 : LGMobileDL Load.
15:55:08 : Port = 4
15:55:08 : Connecting to phone
15:55:20 : Check Phone mode = 1

The program will pause again for a minute and then this will display:

15:55:57 : Phone type check.......
15:55:57 : LGMobileDL.DLL Loading....
15:55:57 : _SetAuthMark Fail
15:55:57 : AuthMark°¡ Á¤È®È÷ Phone¿¡ Write µÇÁö ¾Ê¾Ò½À´Ï´Ù!
15:55:57 : _SetAuthMark Fail
15:55:57 : LoadCDMAPhoneData() Error
15:55:57 : _DetachDLL Call
15:55:57 : _DetachDLL Call End
15:55:57 : Param : Path = C:\Documents and Settings\All Users\Application Data\LGMOBILEAX\Phone\V21E.wdb
15:55:57 : Param : moduleDir =
15:55:57 : Param : waitTime = 33000
15:55:57 : Param : UsbHighSpeed = 0
15:55:57 : Param : PhoneMode = 1
15:55:57 : Param : BinVersion = V21E_00
15:55:57 : Param : AuthMark = 0
15:55:57 : Call fn_StartUpgrade

Last you will hear your USB disconnect/reconnect multiple times while seeing this spammed; this will keep going until the value of "lParam = 100"

15:56:07 : CDMA: wParam = 2006, lParam = 0
15:56:07 : Model Dll Msg Not Found(2006, 0)

Once the program has reached 100 your phone will reboot displaying the LG Logo and after a few moments it will boot up running the chosen baseband.