If you have an iPad 3G and have a SIM card that you want to cut down to a MicroSIM card, you can do just that. Apparently all you need to convert the iPad 3G to U.K. cellular standards is a meat clever. You can also use scissors.
This U.K. resident was faced with a disparity in SIM cards once he received his iPad from foreign shores: “This morning, my shiny new iPad 3G 64Gb arrived from the USA! The only problem was, it had an AT&T MicroSIM and as yet there is no such thing in the UK.”