You will have to JB and unlock it.
Let us know the firmware you're on at the moment.
If you're on 3.1.3 chances are you wont be able to unlock it yet but there is hope down the road after 4.0 is officially out.
Cant unlock it right now.
Give it a few more weeks or less and there should be tools available.
You will be able to update it to official 4.0 and then JB and unlock it.
But that solution is not permanent. If your Father accidentally updates it thru itunes when a new firmware is out for the phone it will lock up again.
Yes, thats worth a try.
A very small percentage of 3G models that were first released had that early bootloader and can be downgraded to unlockable baseband at any time.