I used my droid in Japan, but turned off data, and only used wifi and stored data on the SD cards. I had voice CDMA coverage in quite a few places in Japan (Sendai, Kyoto, Nara, and lots of Tokyo). Dunno about the data coverage since I had that disabled.
I mostly left my CDMA voice radio on to let the GPS work better, but I had offline maps stored on my SD card, along with waypoints. No routing/nav, but you can see where you are, and where you waypoints are, and navigate the old fashioned way of figuring out where to go based on that.
I used Maverick Pro for offline maps, and downloaded google maps using atlas creator before I went.
I didn't have to bother with driving since we got rail passes while we were there, so we didn't need voice directions.
Using 3g data over there could be pretty expensive. I posted quite a bit about it on various droid forums, including this one if you go searching.
Coverage will probably be iffy (depending on where you go within the country) as well as expensive. A nav app that stores maps (not Google Maps Nav) locally would definitely be the way to go.
A little off topic, but FYI. Very few places we went to had wifi, but many of the places we stayed had ethernet connections.
We took a travel router with us, and it definitely was a lifesaver (we were making wifi SIP calls with the droid). Might want to check with your hotels and ryokans you might be staying out to see what their 'net situation is.
Thanks for the info. Verizon told me that they have a program that will give me unlimited data and email for a little over $2.00 a day. I think the program is called Global Access and costs $65 a month. If you sign up for less that 3 weeks, they prorate the monthly charge...comes out a little over $2 a day.
The voice rates are pretty pricey, but, I can get by without CDMA voice as long as I have email.
