Not sure where the OP is from, but you are working on the assumption that he is from the USA?
It is possible to cut down GSM sims and transform them into micro-sims, there are even custom kits for doing it. I'm sure what you are saying is correct, but not globally.
"
The connectors are the same and it has the same thing inside its just that the plastic is much smaller, said Lok8us Haas, adding that SIM card manufacturers slice the same cards down to one size or the other depending on which one its client requests.
That iPad owners will likely consider taking a razor to the plastic SIM cards inside their iPhones, just so they can use the same portable data plan theyre already paying for, should tell you everything you need to know about the wireless data industry."
So assuming the slicing the card down thingy works you could :
1. In the US - Slice your Iphone AT&T chip and use IPAD with full 3G without having to buy an additional plan or slice your any other carrier chip and get 2G (EDGE) speed on your IPAD.
2. Outside the US - Depending on what frequency your carrier operates 3G on, you could slice your regular GSM chip and get 2G/3G speed on your IPAD 3G. I am in Costa Rica right now and my carrier operates 3G on the same frequency as AT&T (850 MHZ). So if the slicing thing works, I would buy a regular 3G line from my carrier, slice the chip and put it in and have 3G on my IPAD no matter where I go