This is not a great solution. Go to Organization/Overview. Click on the "Devices" tab. Click on the + on the right hand side and add the column "Uplink IP (Port 1)".
If the device is "up" and it has no primary IP address then the primary WAN/Internet interface is down. Click on the column name to sort the column. Sort it so that the sites with no primary WAN IP address are at the top. Now you have a quick and easy way to see sites on 3G.