technically, I don't think the carrier is legally aloud to distinguish between regular data usage and anything else. If there is a way for them to. On my network I create a Modem connection that dials #777 and the logon info is my BIS name and password.
I wouldn't use it as a primary connection, I'm sure if they see massive ammounts of data constantly coming thru they will figure it out. I only use mine if I can't find a free WiFi for my latop.
Sprint charges $15/mo for phone as modem, dunno about other carriers. I've never tried the trick of setting of your laptop to dial through the phone as modem to #777, interesting. The bandwidth would be pokey by today's standards...
Mine consistantly gets 850+k on speed tests. Not bad speeds at all I don't think, especially for checking email and general surfing. I remember playing games on slower speeds back in the day.
But then again, checking email is the main intent of a BB....now i have no clue why i would want to tether....