We often get questions about voice SIMs for visitors; this post will serve as the answer.
National law restricts mobile voice plans to residents of Japan. The only way for a visitor to get mobile voice service is to use a rental phone or SIM card. SIM cards can be complicated by the fact that many overseas Android smartphones don't display the required certification mark (giteki 技適) for radio transmitting devices, making them (technically) illegal to use in Japan.
The reason that we don't have any posts or information on rental is because we consider it to be a total waste of money and can't recommend rentals whatsoever.
The average visitor to Japan simply does not need traditional cellular voice, and if you do for some sort of serious business, then you are not the average visitor. You may rely on a voice plan back home, but in Japan, we rely on mail much more than voice - many people almost exclusively. Don't annoy the locals by actually calling them – be cool and send an email ;)
EVERYONE you would contact in Japan can receive your mail. I don't mean SMS, I mean regular email. If you need to call back home, use skype or Google Hangouts or some other VoIP-based solution with free wifi (yes, Japan actually has that now at Starbuck, 7-11 and I think even some vending machines) or a data-only mobile plan because these carry no legal restrictions requiring residency.
We recommend the JCI b-mobile visitor SIMs, which can be picked up at the airport, for data connectivity that is a balance between value and ease of set up. If you want the absolute best deal, get a pre-paid b-mobile SIM from a large electronics retailer for about ¥3,000 for 30 days. These are a better value but require activation with a Japanese mobile phone.
Regarding the lack of certification mark on overseas phones, note the usage of the word technically above. You'll need a phone that support UMTS-2100 MHz (Band 1).