Quickly Cancel Sending a Message by Turning on Airplane Mode
Have you ever typed a message, hit Submit and immediately regretted it? OS X Daily indicates that if you are fast enough, you can turn on airplane mode to cancel sending this message.
While the “Sending …” message is still displayed at the top of the messages, you can go to airplane mode (pull down the Control Center and tap the airplane icon) to cancel the message (this should work fine on Android. Too). If you catch him in time, you will receive a “Not Delivered” note. Due to the size of the message, this works best with multimedia messages, but if you are fast you can catch texts as well.
How to Unsend a Message or SMS from an iPhone | OS X Daily