Try checking the article at
Global capabilities - The DROID Wiki — should give you a basic idea of this.
Yes, that it a useful page. In summary though, data is really expensive if you use the Vodafone SIM. The only real advantages are:
a) you get to keep your US number while out of the country
b) you don't need to get multiple SIMs if you are going to several countries (although some other third-party SIMs also work in many regions)
So what does "really expensive" mean? Here are the current rates (also linked from Gasai's page above).
Canada and Mexico: 75MB for $30 per month, or 200MB for $100 per month, with overage at $2.05 per MB (Canada) and $5.12 per MB (Mexico)
Caribbean & Europe: 25MB for $30 per month, or 70MB for $100 per month, with overage at $5.12 per MB
Everywhere else, no plan, just $20.48 per MB.
If you turn off data everywhere and use Wifi, you MIGHT be able to stay within these limits (but 25MB is very low!). Foreign SIMs are generally MUCH cheaper, I get 25MB per DAY for about $4.50 per month in the UK for a pure PAYG SIM, and with 30 day contracts there are much better deals.
Same applies to calls. VZ charges around $1.29 per minute from Australia and much of Europe, with a value plan (where you pay a few dollars per month) this reduces to $0.99 per minute. I can make calls to the US from the UK for 6cents per minute (or 12 cents to other UK numbers, yes, it is cheaper to call the US than call the UK!)
So, the cheapest thing to do is to get the phone unlocked and use local SIMs. Regional/International SIMs are generally cheaper than the VZ rates, but are more expensive than SIMs for individual countries.
