On my trip to the Philippines my plane stopped in Nagoya Japan. Much to my dismay, my cell phone didn't work. Try as a may I could not figure out why I had no service.

When I got back to the states i did some research and discovered that all of the cell networks in Japan and South Korea are 3G and my 2G phone could not connect to them.

I had an old BlackBerry on the Edge 2G network and it was "no joy" in Japan as far as connecting to their network was concerned.

If your going to be traveling to Japan or Korean and want to use your phone you will have to have a 3G or better phone.

Alternative is to get a prepaid phone when you get there or get a calling card.