It is always a hard decision when traveling internationally on how much bandwidth to buy on the iPad international plan. It is very costly at a dollar or more per megabyte. However, for now at least, buy the smallest plan and use as much as your US plan will allow. I have the AT&T iPad unlimited plan and therefore for an extra $24.99 per month I can get unlimited international minutes!
I am not sure if this is true for any other country except for Canada. However, I have verified it on my two trips and have heard from another person that he experienced the same behavior.
In May I tried to connect to the cellular network in Canada without buying an international plan. That did not work. While at a hotspot in Yellowknife I signed up for the 20MB plan. At the time I had the 200MB US plan. While I was in Canada, I watched my US data plan continue to decrease in available bandwidth while the International plan stayed at 20MBs. Once my US plan was depleted the international plan started ticking down. When I returned to the US I had to replenish my US data plan even though I still had minutes in the international plan.
I signed up for the unlimited service after this trip. Two weeks ago I went back to Canada. Again I tested using the iPad without purchasing the international plan with no success. Again I purchased the 20MB plan and although I used the cellular network extensively while I was in Canada (Edmonton, Vancouver and Regina on this trip) not a single MB was deducted from my international plan.
I have been home for a week and still have a full 20MB available in my AT&T iPad International Plan. Very nice of AT&T to offer unlimited international iPad bandwidth for $24.99 per month!
Update 28APR12 – This is no longer the case. On a recent overseas trip I found that AT&T has fixed this so that international use debits international minutes…too bad for those of us with unlimited minutes.