I finally did it! weew!
I now have my PDA : i900DXIA5/DZIA5, PHONE: i900DXIA2.
Here what i did:
1) Download the official samsung omnia updater for Singapore.
2) Run the i900_EXEcutor.exe to separate the LOADER, PDA, CSC, and PHONE binaries.
3) Run the USDL_GrandPrix_v1.6.4_VISTA.EXE and populate the LOADER, PDA, CSC, and PHONE boxes with the binaries from step 2.
4) Click Detect and turn on the phone.
5) Downloading begin..... This is where i got my 1st problem. The PHONE update failed.
6) Disconnect the cable and reset the phone.
7) Check the PDA version and it's now updated. But PHONE version still i900DXHH3.
Turn off the phone.
9) Get back to the original samsung omnia updater exe file and run it.
10) Activate the Window Mobile Device Center and Turn On "Allow USB Connections" and "Allow data connections on device when connected to PC"
11) Tick the 2 check boxes, turn on your and click verify device.
12) A prompt with Incorrect Software Version will still appear. Click Ok.
13) It will download something (not sure what it is but may the boot loader).
14) it will prompt you to manually turn on your phone. I tried turning on and off, but nothing happened.
15) Exit the omnia updater and turn off the phone.
16) Run again the omnia updater and instead of the 2 check boxes we now have 3. The 1st 1 say for emergeny update only. leave that one unticked but tick the other 2.
17) Click on Verify Device and turn on your phone.
18) Downloading will start... from 1st to 6th files. Just wait until completed.
19) All done.
I used the official samsung updater file