The other thing that we use this for sometimes in order to get us out of a pickle when the voice network at a customer site doesn't have internet access is to set our LAN interface to be the same IP address as the controllers default gateway, and then bridge the connection to the tethered device, and plug directly in to the front of the 3300 (you have to do this out of hours obviously), and then update the licencing through the tether.
Once all done unplug from the 3300 and plug it back in to the LAN, and you now have updated online licencing.