I'll second the question - where are you going? Unless it's one of a handful of countries in Asia, you won't need to worry as there isn't any CDMA signal to be found - most everywhere else uses GSM.
Your phone will be a PDA only. Might as well put it in flight mode when you're not using data. It will happily kill its battery trying to find towers that are 6K miles away
Also, just to make it even more fun, even wifi has additional channels in non-US locals, so there's a slight chance you won't be able to connect via wifi.
All that said, just turn off the radios you don't want to use as others have said.