This is tech-rumor at the moment, but if you are thinking about going to a smart-phone, this is at least worth taking into account.
http://www.engadget.com/2010/07/20/...-style-limited-data-plans-later-this-mo/"...we're hearing that Big Red intends to move to some sort of tiered bucket strategy on July 29."
We have been talking about upgrading my lovely bride's handset, it may be time to bite the bullet.
FYI - I have a grandfathered unlimited data and unlimited tethering plan from ~ 5 years ago, so grandfathering can be a big deal over time.