I have a new iPad with retina display (Wi-Fi only). Can I use 4g with it if I put it under my AT&T contract?

I use my WiFi at home or where available. When I purchased my iPad the sales man said that most places have WiFi available so I really don't need a plan, and if I can't use my iPad to look something up I have my iPhone to use. Well I use it more Than we thought I would be and it's becoming a hassle when I can't connect to a WiFi hot spot. I was wondering since I have AT&T if my iPad is capable of 4g service since its only a WiFi or if that's something that is part of the software.

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