In order to use your own cell phone reasonably in Japan, while you are on travel for 1-2 weeks, one of the best ways is using b-mobile SIM card.

If your cell phone is unlocked, you can use this SIM card and use data in Japan.  The price is:

1GB prepaid for 14 days @ 3,686 yen

http://www.bmobile.ne.jp/english/index.html

You can either purchase it online from Amazon and send it to your home outside of Japan, or purchase it at Yodobashi camera retail stores in Japan.  This card does not need an activation from a local phone number or passport number.  Just need to install on your unlocked phone.  The other SIM card may require you to call some number to activate from Japanese local line (public phone does not allow to do this).  If you do not have any friends in Japan or you do not own Japanese phone number, this is not possible as a traveler.  This SIM card does not to do that.

This is the data only product, so it does not include the cell phone call or text message plan.   You can use the chat app, like LINE/Kakao talk or Skype call.  However, if you want to make a regular call in Japan, like calling friend’s phone or make a restaurant reservation, you can purchase a call contract from NTT, which is a major mobile carrier in Japan.

It’s around 300 yen per month an additional charge will be billed as you make calls.  The call quality is not that great, but it will do the work for a quick call.

http://506506.ntt.com/english/ipphone/plus/