Adding 3G Connectivity to this project

How would I add 3G WCDMA and HSPA connectivity this project www.blairkelly.ca/arduino-wifly-mini without buying the 3G shield http://www.cooking-hacks.com/documentation/tutorials/arduino-3g-gprs-gsm-gps#get-kits for the arduino? I was thinking of using a Raspberry pi and a USB 3G adapter to receive the packets from a laptop via the internet then a USB wifi adapter to send the data to the Arduino.

Help's appreciated.

Thanks.