Apple just released iOS 8.1. In combination with Mac OS X 10.10 Yosemite, this will add support for answering SMS and calls on your Mac. But this feature is not enabled by default. You need to enable it on your iPhone under:
- Forwarding of SMS
Here are two screenshots of the activated settings. They are in german, but I’m sure you’ll find the settings in the english version as well.
There you need to enable other iOS devices and Macs, which also use your iCloud/iTunes account. These enabled devices will then show you a pin code, which you need to enter on your iPhone. SMS forwarding should now be active 🙂