Hello everyone!

I just bought the HTC Desire from Telus and looking into whether or not taking it to Pacific Mall to get it unlocked.
I'm also going to travel for a few weeks mostly in Japan and a short day or 2 in other Asian countries soon.
So what I'd like to find out is:

1) Will an unlocked Desire work in Japan, China, Hong Kong, and Taiwan if I purchase a new SIM card in each place I visit?
2) If I don't unlock the phone, does my phone still work in those places through Telus?

Thank you so much in advance for your help!!

-SF