This will weed out users who just don't care; it will give more information to advertisers as well.
Oh and what's that? 75 cents per month actually ends up tripling their income! (if they now get $9 per year off the seventy-five cents, plus the same four in ad revenue.)
Anyway if even 75 cents per month is too much, then they can go ahead and make OEM deals etc for a facebook sticker and do like Microsoft did. Or give it away with cans of coke. One in twenty wins a year of facebook.
Or, you know, do what people expect and roll into the price of a cell phone.
Just some thoughts...