Fring should work fine. I just got back from Japan, and used sipdroid to make a number of calls. Obviously there was some lag as I was on the other side of the world calling the US, but it worked just fine. Fring should be very similar.
Your GPS WILL work, however for it to get an initial position fix (might take a little while), the CDMA radio *has* to be turned on. It doesn't matter if there aren't any CDMA towers there, or roaming, the radio itself just has to be turned on for the GPS to be able to get the initial fix. You might want to download "GPS Status" app, or use an offline map app.
Once you have your initial fix, you can flip airplane mode back on and the droid will keep the fix active. You might want to manually turn off data by entering in the phone dialer (4636 is info btw):
*#*#4636#*#*
Select "Phone informations"
Hit the menu button
Select "More"
And select "Disable data connection"
You can redo the process when you get back to re-enable the data connection.
What that does is disable the data modem radio, but leaves the CDMA voice radio active.
You can flip airplane mode on and off (to turn off your CDMA voice radio to save battery life), and the data radio should remain off until you go back through the *#*#4636#*#* process to re-enable the data connection.
Of course google maps won't work since you won't have a data connection, but if you use an offline mapping app you'll be able to see the map, and where you are on the map. No routing unfortunately, but it's a big help nonetheless to see the map, where you are, and where your saved waypoints are (favorite bars, hotels, train stations, etc).
I used Maverick Pro for my offline map program in Japan, and had created an atlas before I left using google maps as the source data, and just copied it and my waypoints file to the SD card. I had a ton of detail in my map for all of Japan, and more detail in all the cities I was going to, and the saved maps came out to under 700 MB of data on my SD card.
Hope that helps, have a great trip.
