At the moment, when you connect to the Cloud/BT WiFi Network, it registers you with a Mac Address and a phone number. Your Mac Address is assigned to your handset, meaning you can only connect to those wifi providers using the iPhone.
From the new update, when you make your iPhone a dongle you will have one added Mac address for the laptop/computer of your choice on the Cloud network.
What that basically means is that you can use your iPhone device on both BT/Cloud Unlimited without any problems, but when your iPhone become a dongle and your laptop becomes the device you can only use the cloud because BT aren't letting us add an extra Mac Address...
I'm sorry if it's not any clearer, it's hard to explain lol