Siri will transcribe your messages for you
Apple is making Siri more personable and useful to people who like speaking into some circuits with no other humans involved. Siri will be answering your calls for you, as well as transcribing messages, so you don't have to listen to them.
Say what? Let us explain.
Well, old people like listening to voicemail messages, while younger people have zero interest in someone blathering on in a recorded message. So, with that, you'll be able to tell Siri to write them down for you. As for answering your messages, if you're away or somewhere with very little signal, you'll be able to instruct it to reply to people, explaining why you can't take certain calls.
Obviously, you could just rerecord your own voicemail message, but if you're using the iCloud voicemail, you have the option of letting Siri do it for you, instead of letting the call go to the standard digital audio recording.
And when is this happening?
Well, it is thought that this will become a thing some time next year in 2016. You can assume that this will coincide with a new version of iOS, along with a host of other new features for your Apple devices.