As an American, what type phone do I need to buy if I want one that works in Tokyo, Japan AND Shanghai, China?

Question:

I think all I need is a "quad band, unlocked" phone and just get a sim card when I arrive at each place. However I've learned that Japan doesn't "do" GSM, just "3G". Does that mean I need a "3G quad band unlocked phone"?

Answer:

I cannot speak for China, which is suspect to be a GSM country, but for Japan you'll need something that is WCDMA / UTMS capable on the 2100 MHz frequency.

For Japan (as a tourist) you cannot show up and purchase a sim card (you need to be a resident of Japan to do so). You can however either:
1. Rent a sim card and pay a rental fee
2. Just rent a telephone (you can rent iphones, and other phones at the airport, on daily or weekly plans).