Ever receive a phone call in a meeting or in the middle of something that you're unable to answer?
In case you didn't know, your phone gives you a quick option to easily send a text message to that person while declining the call. When you see that you're getting a phone call, tap Message (iPhone), or Send Message (Android), then tap which text message you would like to send to the caller, such as "Can I call you later?"
If you would like to craft your own message, tap Custom, and text and send your message as you would normally. Now that you have notified your caller that you will give them a call back, you can go back to carrying on with your meeting or what you were in the middle of doing.
This feature works when you respond to a smart phone but not a landline phone, which normally does not support text messages.