b-mobile worked great for me a few years ago in Japan (I had to find the SIM card at a Bic Camera shop myself - Narita/hotel delivery is definitely an awesome improvement) and I’m glad to hear they’re doing well. A few years out of date (2010) but I did a writeup of getting mobile data around the world when I was doing some traveling. Japan was actually one of the tougher ones (Softbank SIMs were charging at $31/MB w/ no cap for data!): http://randomfoo.net/2010/07/19/mobile-data-while-traveling
For those looking for a comprehensive resource, the there’s a Pay as You Go Sim with Data Wiki that’s pretty well maintained. I’ve found that data in Europe is usually ridiculously cheap (oftentimes 500MB or 1GB is given away w/ the SIM) and these days I tether with my Android handset w/o problems (and always have a spare battery/charger handy).
Looks like Orange currently sells data-only SIMs for €10/GB in France, and as mentioned 3Mobile has a month of unlimited data for £15 in the UK. I picked up an Orange SIM in Spain and an O2 SIM in Germany recently (which came w/ 500MB of data free) and had no problems getting things running in minutes.
