google voice and skype do not work over voip or international data. unlesss theres some hack i don't know about.
to prevent data charges, go to your settings and turn off data while roaming.
but heres the thing... international data is 60 a month. and you can turn it on when you leave the country, and turn it off when you get back. normal data plan is 30/mo, so considering that, its only $1 more per day.
i was in asia for 10 days, turned it on when i left turned it off when i got back. only $10 more on my bill. sooo worth it, i used an insane amount of data.
and if you do follow that, make sure you turn on unlimited international data. just turning it on international data you will pay by the kb, and forgot the amount but it amounted to $20/mb. insane. $10 i used close to a gig in my 10 days and got charged $10. funny even tho you turn it on you get random text warnings. i called verizon to make sure i had unlimited on because i got a text saying i've incurred $1000.00 in data charges, but they said don't worry cause i had it on and it was just a standard warning text.