Short answer is yes, however there is an extra step involved to set it up.
All of the PVR's that support both the IceTV Guide and the IceTV Interactive service have a network connection built-in. While they will also have a USB port, this cannot be used for a 3G wireless internet connection.
This does not mean you cannot use the 3G connection to get your PVR online. The best option is to get a wireless 3G router (one option is the Netcomm 3G17WN 3G Wireless N150 Router that is available in the IceTV Online Store. This router can then be connected to your USB 3G modem, and also via a cable to your PVR. It also has the ability to share the internet connection wirelessly so you can still use the internet on a laptop (or desktop computer with wireless) anywhere in the house.
If you are concerned about how much data is downloaded by IceTV each month you should have a look at How much of my internet quota does IceTV use each month?