Last year, I travelled with my Canadian iPad to the US. I bought the sim and prepaid Visa, but i wasn't travelling with my laptop. When I inserted the sim and tried to activate nothing happened, since you needed to have the carrier information downloaded in iTunes.
In some of the postings here, people have said that the activation can be done directly from the iPad - no computer.
I wondering if the IOS upgrades over the past year eliminated the need for having the laptop around.
I traveled abroad with an iPad 1 almost immediately after its debut and had no problem switching SIMs and activating 3G service without a laptop or PC. I suspect that your problem was tied to the carrier, rather than with iPad.
I went into a carrier store overseas with my iPad 1 for the first time, signed up for 3G and it was functioning before I left the store. In other cases, there's sometimes a carrier delay of up to 24 hours in some countries, and some just haven't got enough sales people trained to help customers with hiccups.
In the U.S., it's best to call the carrier's 800 number if you've run into snags at a store. If you get someone who's unfamiliar with your problem, hang up and try another rep. It's sometimes luck of the draw, because each rep's experience and exposure differs, despite general training that's supposed to be the same.