First I want to mention that this post on Cocoanetics.com was what started it all for me...
I'm planning my yearly vacation to Virginia Beach coming up in 2 weeks time, and I wanted a Data plan so that I could access the internet during the 13 hour drive down there.
There are a few sources of information for this project, and I wanted to share my own experience as of July 2011.
At the moment, I've found only one valid solution to having 3G data available in the US without paying the horrendous roaming data fee that Rogers (or any other carrier) charges : the GoPhone prepaid SIM card from AT&T.
If you're ok with Edge speed, then you could also go with Simple Mobile, which works on the T-Mobile network and thus only provides Edge data.
The first step is to get your hands on a GoPhone SIM card. If you search on Ebay, you'll see that there are SIM cards available from US sellers for anywhere from $5 to $10 shipped. As I was not willing to risk the SIM card not being shipped in time for my departure, I decided to drive down to Plattsburgh NY instead, which is about a 1-hour drive from where I live.
I first tried to get the SIM card at Walmart's, and then Radio-Shack, but they didn't sell the SIM card without an accompanying phone. I then went to the AT&T store on Smithfield road.
As I had read on a couple of sites beforehand, the staff first tried to convince me that the GoPhone SIM card wouldn't work in my iPhone. I told them politely that I looked it up and that I didn't expect them to support me in the process, and they agreed to sell me the SIM and a phone/text plan ($2/day unlimited, minimum purchase $15) as well as a Data plan ($25 for 500MB).
I then rode my car back to the canadian border, told the agent exactly what I had bought, and they let me through.
So I am back home, and later on this weekend I'll proceed with the next step, which will be to cut the SIM into a MicroSIM, then change the APN settings in the iPhone, and finally pop the SIM card in to test it, although I'll be in Canada... we'll see what happens.