Is unlocking mytouch 3G permanent?

[stickydoorknob]

I am planning on travelling to Hong Kong in a few weeks and would like to use my mytouch 3G there. I have read a few tutorials on acquiring the IMEI number and calling t-mobile to unlock it for me, but I am confused as to whether if this unlock is permanent or only to the new sim card i'm using the unlock code for. If the unlock is only for a specific sim card, is there a way to permanently unlock the phone so any sim card will work on my phone? -Thanks