Here are a couple of additional subscriptions:
I carry a Nokia E65 which is a quadband plus WCDMA for Japan and Korea. I use Truphone (
www.truphone.com) which integrates with the phone nicely. Calls to the US are six cents flat. Talk for three hours if you want. I purchase a PAYG roaming account with Boingo.com which gives me unlimited PDA access throughout Europe for $8 a month. Their Japanese coverage is just as good and includes Narita.
The cool thing about Truphone is that you can get a free US phone number with PAYG number forwarding when you are off line. When you are online, incoming calls are free. Plop a rented Japanese SIM card (you can't buy Japenese prepaids) into phone and it will automatically set call forwarding to that SIM when you are out of VOIP range.
Yackie mobile offers a hybrid VOIP/roaming SIM combination which can effectuate similar roaming between your prepaid SIM and their voip service depending on your status.
Magic Jack is popular with many people. Plugs into your USB jack and gives you a voip connection. You can usually borrow a hotel phone and plug it into the RJ11, but a pair of ear buds into your computer will work in a pinch. $100 gets you five years of unlimited calls to the US and US phone number with call forwarding ability.
If you've got TMobile as your carrier, purchase a Hotspot at Home compatible handset. When you are on wifi, calls come out of your bucket of minutes or for $9 a month you have unlimited calls while on wifi.