Can you convert iPad 2 WiFi only to 3G

The iPad 3G is more expensive than the Wi-Fi only mode and you need to buy a new data plan from AT&T. Now I have got an iPad 2 WiFi only and want to use it in my car as GPS tracking. How can I convert it to 3G?If you need to get your iPad Wifi connected to the 3G or 4G network, you can buy a mobile hotspot offering you the internet access. If you have an rooted android phone, just turn it into a