[myTouch 3G, Magic Android Development] Kevbodian:
This method is what I used to unlock my 1.6 Docomo HT-03A. Please don't hold me responsible for any issues you have. I typed this up really quickly as a reference for other NOOBS like myself so that you don't have to scour the board. I don't know where you got your unlock code from, but if you have one, you may follow these steps to get your device unlocked.

* - Note: If you are running Docomo's Donut ROM (1.6) then when you insert your non-Docomo sim, you will NOT BE PROMPTED to enter your NCK (network unlock PIN). These steps are necessary to get back to 1.5 so that you can get the unlock PIN entry prompt.

Before this process your FASTBOOT screen should look like this:

SAPPHIRE EVT1 32B SHIP S-ON G

HBOOT-1.33.0006 (SAPP20000)

CPLD-10

RADIO-2.22.19.261

May 27 2009,19:06:41

1. Install Android SDK. On windows it's just a folder. From the TOOLS folder, copy Adb.exe, AdbWinApi.dll, and fastboot.exe to C:\windows\system32\. Next rename the SDK folder to something convenient and place it at C:\XXX where XXX is por... where XXX is whatever your SDK folder is called.

2. Make sure ADB is installed correctly. Once you think it is, open a command prompt and type:

adb devices

You should get something under "List of devices attached". If not, your drivers are not correctly installed.

3. Using a Micro SD make a Goldcard. I used the video here.

3.5. Download and install any 32B rom your heart desires, and copy it to the root of your SD card (your goldcard); this will be used later.

4. Fix your Perfect SPL. The docomo SPL is HBOOT-1.33.0006 (SAPP20000). Go ahead and follow Amon_RA's steps here.

Use the Engineers SPL on that page (ROM v2.53.707.2 (Engineerings SPL v1.33.2010) - MD5 : F9674D19BE5F949D0D9DC99714D210E3).

5. Boot the phone normally, and if you have a non-Docomo sim to insert AND you have your unlock code, you may now enter it the the device will be unlocked forever, yay!

6. Turn off the device and check your FASTBOOT (BACK+END) screen; it should look like this:

SAPPHIRE EVT1 32B ENG S-OFF H

HBOOT-1.33.2005 (SAPP20000)

CPLD-10

RADIO-3.22.20.17

Apr 20 2009,15:30:43

Note that the device is rev EVT1 32B ENG S-OFF H: a 32B model with board rev. EVT1, ENG = engineering version SPL, S-OFF = security off (simlock off?), and H for HTC.

Note that Amon_Ra's G-type recovery images WILL NOT work at this point.

This H and the radio below are for 32A devices, which leads us to step 7.

7. Revert to 32B radio and G recovery. Steps found here under the section "Revert to 32B Radio and ROM". The radio can be found here.

fastboot flash radio radio.img

Press menu to POWER OFF. Then re-enter FASTBOOT (BACK+END) and check that the radio has been reverted.

fastboot erase system -w
fastboot erase boot
fastboot erase recovery
fastboot flash recovery recovery-RAv1.2.0G.img

*** - Note that instead of recovery-RAv1.2.0G.img, you may use the newer recovery-RA-sapphire-v1.6.2G.img instead.

8. Press MENU to POWER OFF. Hold HOME+END to boot into recovery mode.

9. Install update from zip inside recovery mode.

10. Reboot or allow the device to reboot and enjoy your device.

edit: My FASTBOOT screen still has SAPPHIRE EVT1 32B ENG S-OFF H instead of SAPPHIRE EVT1 32B ENG S-OFF G. I wonder if I can just change my SPL back to the original Docomo ship one or if there is some ENG SPL S-OFF G available somewhere?