BlackBerry cannot Unicode UTF-8 characters, I wonder there's a way to make this possible ?

It has been able to for quite some time. You have to select the correct language that you're trying to use. OS version 4.2 definitely does, I would guess 4.1 does too.

Truely, BlackBerry cannot display vietnamese which is normally unicode utf-8 encoded.

It's cannot display this correctly on BB's phones: Chào bạn, tôi đang viết tiếng việt.

You can see, the words would broken.