Even though your iPad 3G comes already loaded with a Micro SIM Card, you don’t necessarily have to use it, as the iPad 3G is contract-free and can be used on most wireless networks. You may want to use your current mobile phone provider, especially if you live abroad and bought your iPad 3G on the grey market.
The guys at Secret Lab simply used nail clippers to cut a normal SIM card to match the Micro SIM card’s dimensions, and got their iPad 3G to work on their local 3G network, in Australia.
Note that you may want to check with your wireless provider about how much data you are allowed to use before you download zillions of applications. Also, note that the iPad 3G does not necessarily work on all 3G networks due to limitations around the radio frequencies it can use. In this case, your iPad 3G will likely fall back to 2G, which is much slower.