Would iphone (att or verizon) work in Japan?

Question:

Does it need to be unlocked? Roaming Fee for calls and Data? How does it work exactly? Are there any other types of phone from U.S. that work in Japan? Thank you!

Answer:

iPhone from AT&T or Verizon will work in Japan as roaming.
It does not need to be unlocked.

For Verizon, you need to call the Verizon customer service before you go to Japan and make sure your account is allowed to call internationally and roaming.

For AT&T, you need to subscribe to a free "Expanded International Roaming" option.

The call costs $1.99 per minutes for Verizon, both calling and receiving.
It costs $2.29 per minutes for AT&T, both calling and receiving. If you subscribe to the AT&T World Traveler optional plan, which costs $5.99 per month, the call rate is reduced to $1.69.

The data with Verizon costs an expensive $0.02 per 1KB. There's no international roaming discount rate in Japan with a Verizon phone.

The international roaming cost for AT&T is $0.0195 per 1KB if you don't subscribe to a Global Data Add-On plan. If you subscribe to a Global Data Add-On plan, it will be reduced to $24.99 for 20MB, $59.99 for 50MB, $119.99 for 100MB or $199.99 for 200MB. The excess bytes are charged at $0.005 per 1KB.
So, the AT&T's international roaming data plan is cheaper by about one-fourth of Verizon's if you subscribe to AT&T's Global Data Add-On plan before you go to Japan.
You can cancel the Global Data Add-On plan right after you come back to the USA.

If your account is enabled for roaming, when you arrive at a Japanese airport and turn on your phone, it will receive the SMS text message from AT&T or Verizon welcoming you to Japan with a short message on how to dial in Japan.

Any AT&T smart phone (iphone/Android/Blackberry) that supports 2100MHz 3G frequency will work in Japan as the same way as iPhone from AT&T.
Any Verizon/Sprint smart phone (iphone/Android/Blackberry) that supports 800MHz CDMA2000 frequency will work in Japan as the same way as iPhone from Verizon.

Any newer (3-4 year-old or newer) non-smartphone from AT&T/Verizon/Sprint will work in Japan as voice-only roaming.

Some T-Mobile 3G smartphone may work in Japan.