Rental phone for Japanese use only

i need a rental phone that will work with things like c-mail which is used by au subscribers as well as being able to contact any other people on other subscriber networks within Japan, either by voice or mail. The phone will operate solely in the Japanese language.. I don't need it to contact outside Japan.
Anybody have any suggestions please?
Many thanks
Derek
PS. It's for my wife who is Japanese.

All modern rental phones in Japan will fit your wife's needs. You can either pick one up directly at the airport, or order in advance over the internet which tends to be cheaper and with better selection. Global Advance, Pupuru and Japan Rentafone are often recommended on this forum.