i think you can just unlock it. A friend of mine unlocked the phone so it can be used in the UK.
Try to get it done in the states before you bring it to Taiwan thou. In taiwan, I brought my SE w580i to a store and asked them to unlock it for me, and they made it sound so complicated. like it might ruin the phone and they`d have to send it elsewhere blah blah blah.
I came back to Vancouver and called up a cellular repair shop to see if they could unlock it for me. they said it`d cost 20 dollars and i`d be able to use it anywhere.
Anyway, so becareful of who you go to. Find someone trustworthy and you should be able get it done