Apple iPad with Wi-Fi – You can Connect to the Internet wherever you can access a Wi-Fi hotspot. Some restaurants and coffee shops provide free wireless internet access. All iPad models come with built-in Wi-Fi.
Apple iPad with Wi-Fi + 3G – You can Connect to the Internet wherever you can access a Wi-Fi hotspot and also over AT&T’s 3G network, the networks which is used by mobile phones. This model is is good when you’re not within range of a Wi-Fi network. 3G data plan service sold separately. Checkout iPad 3G Data Plan – AT&T Pricing.
You are not required to purchase a 3G data plan when you buy an iPad model with Wi-Fi + 3G.