Official Sites
NTT docomo, au by KDDI and SoftBank offer content providers to register an official site (or 公式サイト), which can use extra features such as carrier billing.
Becoming an offical site is an involved and difficult process.
docomo
More information on how to create an official site (公式サイト) starts here: http://newip.nttdocomo.co.jp/
au
More information on how to create an official site (公式サイト) starts here: http://www.au.kddi.com/ezfactory/kijun/hajimeni.html
SoftBank
More information on how to create an official site (公式サイト) starts here: http://creation.mb.softbank.jp/partner/cp_reg.html