I agree on the NTT aspect. Get Vodafone if you're only there for a
short stay. They do prepaid phones. As far as I know, NTT only does
subscription and although technically their handsets are good, you pay
for what you get -- charges are very expensive. I wouldn't touch au
either personally because their charges are also high. Check the
handset does English before you choose, some of them are Japanese only.

Also, because it's assumed the Japanese don't want it, Japanese handset
and mobile services often don't play nicely with international
connections. Some companies block them and require special
registration, so check when you buy.

One thing about Japan, most of the hotels have FREE (i.e. included in
the price) broadband internet access. This is true for some business
hotels (about $100 a night) and right up to places like the Hyatt. I've
no idea why this is, but perhaps it's a competition thing. In any case,
it makes staying in Tokyo very easy. Just make sure you've got an
Ethernet cable with you.

Check whether your hotel