Regarding data charges...
For those of us who do not reside in the USA, if we don't have an unlocked phone or use our home provider even when traveling with an unlocked phone, when we come to visit your fair country we have to pay for data through our home provider, not through whatever local providers you have. This is called "roaming data". There have been reports of data charges in the tens of thousands of dollars for people who travel without making appropriate plans before leaving.
In my case, I have a data plan from Rogers that allows me to roam into the USA without additional charges, but the largest data cap available is only 500MB/month, which is not very much data depending on usage [streaming video can eat up a lot of data]. My plan costs the same as a Canada-only 500MB data plan plus $10 to allow roaming in the USA. If I travel to elsewhere in the world, I have to prearrange for a data plan that covers where I'm going and how much data I expect to use.
A one-week data pass for roaming in the USA costs $100 for 250MB.
A one-week data pass for roaming internationally costs $225 for 75MB.
For customers who have domestic Data Plans, data roaming in the U.S., Puerto Rico or the U.S. Virgin Islands is $0.006 per KB, or approximately $6 per MB.
Data roaming without any plan at all costs $0.03 per KB - or approximately $60.00 per MB.
All of the above are based on current Rogers rates for data. As you can see, traveling with a smart phone could get very expensive very quickly if you don't plan ahead.