Android: Google's awesome voice commands have been able to send text messages for a while. With a recent update, however, you can finally do the same with Hangouts instant messages.
The update allows users to say "send a hangouts message" to send IMs to other users, hands-free. The command works like most others. Google can ask you for each part of the command (like the message itself and who to send it to) individually, so you don't fumble with a long, complicated command.
Google Now Lets You Send Hangouts Messages Using Voice Commands [Android Police]