The iPad is like a cell phone on steroids or a laptop on a diet, depending on how you want to look at it. It is a mobile computer; mobile like our cell phone, but not as big and bulky as our laptop. It is what is called a “tablet”. The screen is much smaller than a laptop screen and substantially larger than your cell phone. It is more along the lines of a netbook, only an inch or two larger. … To connect to a 3G network, the user must insert a 3G SIM card from a service provider. …

Link:
Explaining The iPad