I followed the how to for dun connection and got it to work. My question is if I am not on a tether plan will it cost me extra to use it this way? I am on AT&T with a bb 8310.

It they catch you, they will charge you for past use... I would say that occasional use probably won't get you caught... but regular use will.

If you are going to use it on a regular basis I would add it.

And those retroactive charges can be a killer.