I'm currently doing it as I type.
for the instruction.
Long story short. To make it easy :
1. Flash AT&T 7004 ROM
2. Unlock & Prevent Relock
3. Open Diagnose Mode ##634#
4. Install New_SMS_Unlock.xap
5. Install Samsung Root Tools from Heathcliff
6. Use the Samsung Tools to create provxml folder in root directory
7. Find unlock.xml from Applications folder and copy it to provxml folder (details on how to do this can be found on the the thread above)
8. Upgrade to NoDo (7390) Don't Unbrand !!! No need to go to 7392, and you won't get update for Diagnose if you unbrand.
9. In 7390, Uninstall your Diagnose app.
10. ##634# again, and your diagnose app will be updated.
11. After this make sure you can read the unlock.xml using *#9908# from Diagnose. If you can see your unlock.xml then you're good to go, if not then you must be missing something.
12. Flash to 7661
13. Open *#9908# from Diagnose.
14. Choose Unlock and press Save.
15. Your 7661 Focus should be unlocked by now.
Credit goes to original owner of the thread above and everyone whose contributing.
Sony Ericsson T100 > Motorola C380 > Mitac Mio 3830 > Samsung E730 > Motorola E680 > Motorola MPX200 > Dopod S300 > Nokia N76 > Motorola Droid > Blackberry Tour 9630 > Palm Pre Plus > Samsung Focus > LG Optimus 2x > Nexus S (I9023) > Sony Xperia U ST25i