I'm no fan of Qwest, but I haven't had the cost creep you mention since buying into their unlimited long distance plan quite some time back. The sent me a letter to explain the new plan they had, which was 5 cents a minute, with a $20 cap, a better deal than the $20 unlimited for people that may use less than 400 minutes in some months.
They also sent me a letter later on stating that their would now be a monthly fee if useage was under a certain amount, but I always use more than 400 minutes per month so always end up at the $20 max that they charge for LD anyway.
I guess I can't recall ever having them just raise my rate without notice, and I've been a Qwest/US West customer since 1993.