Thanks for the info, SfumatoPants. I'll try the Boingo option first, as it's free for the first month in any case, and unlike the Hot Spot doesn't charge a registration fee. On line registration is only available if one has a Japanese address in any case. Looks like a day pass (at Y500 per 24 hours) from Family Mart will work if Boingo doesn't work out. There is this somewhat disquieting note at the Hotspot site: "* Please note that 1-DAY PASSPORT can not be used at Tokyo Midtown and roaming service areas." Any idea what this means? There's no search function on the English version of the Hotspot site, but there may be more info on the Japanese version.

I'll post back about my experience when I return.