As noted by others, Tropo works worldwide. We've got numbers in 30 countries and 8 different European languages for text to speech. If you want a number in a place we don't list, let us know and we'll see what we can do.
We already offer phone numbers in Japan. Some Asian countries don't allow voip services to operate or have extremely high costs. So it depends on where in Asia you're looking. From your Twitter profile, looks like you're in Singapore. We can get you a number there but they are fairly expensive. Feel free to send an email to Tropo sales or support and we can figure it out.