Just my .02 - enjoy the vacation, and turn off the phone
Having said that, I agree with idroid, you can/should look at the international roaming rates for the countries you will be in, but I suspect they may be pretty high.
I recently went to the UK, and there is no CDMA service available there at all. Thinking I would be able to find WIFI service, I researched a bit, and decided to try Fring to be able to do text and VOIP calls. I tested it here, and I was able to send IM (fring, MSN messenger, etc, not SMS by the way) and call other Fring users free using VOIP.
Fring supports Skype out, so you should be able to call other Skype users for free, and assuming you have Skype credit, you should be able to call any number relatively cheaply (I think for most places its $0.021/min). I did not test this.
In practice, it didnt work out too well. I could not find free WIFI hotspots. When I did get connected, IM worked, but as soon as I tried to make VOIP calls, they just dropped. Im not sure if it was user error, or if the wifi provider had somehow blocked VOIP.
My experience with the WIFI on a cruise ship (Princess) would indicate that it might not be a viable choice either - it was QUITE slow (like SLOW dial up effective speeds). The net result was that I gave up being connected, and just enjoyed my cruise, and I was a lot happier anyway.
BTW : if you do try, you can avoid chancing the roaming charges by putting your phone in Airplane mode, then turning WIFI on. That way the phone radio and data is shut off, and the only connection active is WIFI.
Good luck, have fun!
jc