I wonder why the PC Companion still saying that my phone is updated, in fact it's still 1.6..

Finally, Updated to 2.1, by force..
Those who still can't retrieve 2.1, just follow the guide here http://forum.xda-developers.com/showthread.php?t=825228
just changed the version number of your phone. Mine changed to 1241-4091, russian firmware.

Most important thing, it fixed my wireless frequent disconnected issue and also my phone unable to boot up when Wifi turned on. (eg. turn on wifi, off phone, turn on the phone again failed)
I thought It was a hardware problem, 2.1 solved this and I'm happy 'bout it
Now waiting for the rooting of 2.1, not available at this moment.

That's the thing in my mind whether it void the warranty or not
Maybe, can change back to original number when 2.1 root is available and then reflash it back with 2.1 unrooted. Not sure if they can trace it or not

In Malaysia it's available but not all the batch they roll it out.

This is what I'm thinking of, once the root access for 2.1 available, just changed the code back and then reflash it again. Should be no problem right?

Yes, I know that, once the root access for 2.1 available