Update: There is a new Version of XDA2Unlock (v 2.2 as of this writing) available, which does not require the bootloader or the reset. Please visit http://forum.xda-developers.com/viewtopic.php?t=6963 for information and the download. The setup file is in the forum post.
Only users with Radio 1.05.12 should use the process below:
xda2unlock
A tool to unlock the Himalaya
XDA Developers xda2unlock tool
This program will extract the unlock code from your XDA II.
For this to be possible, a few steps are necessary:
1. The XDA II needs to be put in bootloader mode.
NOTE: THIS WILL WIPE ALL YOUR DATA SO FIRST BACK-UP!
You enter the bootloader by holding the Power button and the Action button
while pressing the stylus in the reset hole on the bottom.
In the bootloader mode, the display will be gray and say Serial at the top.
2. Next put the device in the USB cradle. The display will now say USB
and the first time Windows will detect a new device.
3. Disable USB in Active Sync in 'File -> Connection Settings'
Now the device is ready to extract the unlock code.
Type YES when you have completed the above steps and want to continue: YES
Communication port opened.
waiting for radio bootloader
reading first block...
reading second block...
Unlock code: 2040248
When you insert a blocked SIM in your XDA2,
you can enter the above code in the SIMlock box.
Alternatively, you can connect to the wireless modem
and enter the following AT command:
AT%HTCLOCK=0,2040248,1
Do not forget to enable USB in Active Sync again!
http://forum.xda-developers.com/viewtopic.php?t=6963