Telus Diamond and Tethering

[daoom]

Since my $15 unlimited data plan doesn't cover tethering, I don't want Telus to know that I'm sharing the internet connection. I ran a search and found a few thread on the topic, but what I'm looking is a nice technical explanation of how the service provider can tell tell whether the connection is coming from your phone or if your phone is being used as a modem and how you can prevent them from seeing it.

If there's already a thread with a primmer on this, can you please point me to it since I wasn't able to dig it up.