Very sure

. As I said, I started and accepted calls to my iPhone 4s both with my iPad 4 and my MBA. So yes, it works. At least here, I've read in the forums some people are having difficulties with it.
How that'll work with the SMS, I can tell you in about 24 to 48 hours when iOS 8.1 is released.
According to the Apple presentations the iPhone 4s gets these Continuity-features (done through WiFi).
It does
not however get Handsoff (which is a part of Continuity). So picking up surfing on the other device where you left off, or composing an e-mail or anything like that, doesn't work on the 4s. It does work on the iPad 4. Sad, but Handsoff to me isn't as important as the the phone calls (and hopefully the SMS sending will work with 8.1).
Hope that helped a bit.
Best regards,
VSG