you do have to make sure you buy the 3G version, which means the ipad can hold a sim card. This is the more expensive of the 2 models, the wifi only model does not have the facility to insert a sim card! Apple are still pointedly refusing to include a usb connection so internet dongles are not an option.
I'm not sure if it has to be a contract sim card though.
The wifi only ipad can connect if you are out and about, say having a coffee or some libraries have wifi free zones. Sadly the UK is not so wifi free friendly as many other countries I have visited
