I don't understand why everyone is against metered data costs whether it be on phones or one their home connections. Electricity and other utilities are metered by use and it doesn't seem to provoke the outrage that metering of data connections does.
Adding metered data usage could make the iPhone data plan cheaper for light users. The concept of metered usage is not inherently any less fair than unlimited usage plans, it all depends on what price structure they propose. If unlimited data is $30 but 1Gb/month is $15 then the average iPhone user is saving money, on the other hand if instead the pricing was $1/Mb obviously the users would be losing. It's clearly too early to be worried, why don't you wait and see what happens?
Why shouldn't the people who use a little data on their iPhone pay less than the people who use a lot?