I'm incredibly interested in an iPad, but although it's primary use would be at home, there are times when I would need to take it away from my Wi-Fi comfort spots and out into the wider world. As such, I don't really think I need 3G, and therefore only intend on buying the Wi-Fi model. However, will it be possible for Wi-Fi owners to purchase one of the Micro network cards (or whatever they're called!) afterwards and sign upto 3G later on or as and when required? Or will it be a case that if I go for the Wi-Fi model that will be it?