I also stumbled upon something interesting.. I popped in a friends sim card from another carrier (Fido) last night other than my own (Telus) and magically it unlocked internet sharing!? I was selling it so we wanted to make sure the phone worked ok with Fido and I was just discussing the internet sharing feature while not expecting it to actually work.
I have the Titan 2, internet sharing is locked on my phone but I may try another sim for fun and see what happens.
EDIT: Tried a Rogers sim and no dice.. Wondering if this glitch to enable it is exclusive to the Titan 1 only??