Arduino internet

Hello, I am planning on doing a project for my car where the arduino can monitor the fuel, position of my car and upload it into the internet. Since the car would be mobile, how can the arduino be connected to the internet, if I am using an ethernet shield then wouldn't it have to be connected to wifi or a lan cable. Is there any module which can be used to connect arduino to the net using 3G? or other types of data connection which can make the arduino completely mobile?

Something like http://www.sparkfun.com/products/9607 would be typical.