If you have ios6 installed, the phone will run as smoothly as a new one. Which means you'd have a working phone, working iMessage, working email, working web browser, notes, weather app, 3.5mm jack, clock, iTunes, alarm lock, camera (albeit very low quality, but still), 1080P video, Apple maps, GPS, Siri, FaceTime--as well as a slew of older games, some which don't even run on newer phones due to Apple forcing all the developers to update their games. And all of that in a much more compact size than what's currently available (one hand use, and can fit into even the skinniest of skinny jeans).
That's far better than a dumb phone.