iOS 8.1 enables the Text Message Forwarding feature (also known as SMS Relay) that was first announced alongside iOS 8 and OS X Yosemite at WWDC. Once enabled on an iPhone and other devices signed into the same iMessage account, this feature allows you to send and receive SMS text messages on any device. It means that you'll be able to reply to SMS on your Mac or iPad, using your iPhone as a relay hub.
The SMS Relay and phone relay features are really exciting to me. One area that Google has been ahead for quite some time is allowing be to talk on my phone through my computer courtesy of Google Voice.