In accordance with Betteridge's Law of Headlines, I believe the answer is a resounding "no."
The unusually virulent meme quickly spread around the Mac blogging world that iMessage will kill SMS as we know it and, going one stage further, to characterize iMessage as "an attack" on the carriers. John Gruber of Daring Fireball went so far as to say he would "cancel my SMS plan as soon as this ships."
But hold on there a second. Is it really that simple? Sure, on the face of it, iMessage has all the ingredients to completely replace SMS. It can send text and pictures and contact vCards, exactly as an SMS can. It's enriched with the ability to tell when the person you're chatting to has received and read your messages, and you can also see when they are typing a response.
It can do many-to-many group messaging too. And best of all -- this is all transferred over your iPhone or iPad's Wifi or 3G data connections, so it's free! Well, at least until you exceed your 3G bandwidth cap and have to pay an overage charge, anyway. It sure sounds like iMessage is going to kick some sand in SMS's face.
But there's a bit of a flaw in this line of reasoning. iMessage is resolutely iOS only -- so far, we've not even seen any evidence it'll be able to interoperate with Macs, let alone work with other smartphones -- even though that means Apple is now shipping three incompatible communication clients (iChat, FaceTime, and now iMessage). When you send a message to someone who doesn't have an iOS device (which it detects based on some sort of deep black magic that sounds similar to the SIP database Apple runs for FaceTime call placing) it falls back to plain ol' SMS.