Some build-in android sms applications do not allow to send blank sms. This application permits sending blank (actually single space character) sms to specified number.
一些构建在Android短信应用程序不允许发送空白短信。此应用程序允许发送空白短信到指定的号码（实际上是一个空格字符）。

Now you can send text messages to single-digit phone No.
Samsung built-in software forbids sending for ex. to 0.